111111111111111111111111111111111111111111111111111111111111111111111111111
usoon08023B2
(12) United States Patent
Reeves et al.
(10) Patent No.:
(45) Date of Patent:
US 7,208,023 B2
Apr. 24, 2007
(54) DRY DUST CONTROL MATERIALS
(73) Assignee: Hazen Research, Inc., Golden, CO
(US)
(75) Inventors: Robert A. Reeves, Arvada, CO (US);
Charlie W. Kenney, Littleton, CO
(US); Dennis Johnson, Arvada, CO
(US)
10/1939 Fife 44/602
4/1980 Dunn 274/47
4/1981 Rich 44/624
6/1982 Hastings 361/228
10/1988 Roe 252/88
11/1992 Lee 55/104
12/1992 Mathison et al. 104/7.3
8/1995 Kondrats 252/88
3/1997 Brown 95/3
6/1997 Brown 44/505
9/1999 Nojima 96/55
8/2000 Eichorst et al. 430/527
3/2001 Fukuura et al. 428/175
2/2003 Varnadoe et 31 106/269
2,176,129 A *
4,198,061 A
4,260,394 A *
4,335,419 A
4,780,233 A
5,163,983 A
5,172,638 A
5,439,608 A
5,607,497 A
5,637,122 A *
5,958,112 A
6,110,656 A
6,207,255 B1
6,514,332 B2 *
(22) Filed: Feb. 14, 2003
( *) Notice: Subject to any disclaimer, the tenn of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 277 days.
(21) Appl. No.: 10/367,576
(65) Prior Publication Data
Related U.S. Application Data
(60) Provisional application No. 60/357,540, filed on Feb.
15, 2002.
(51) Int. Cl.
C10L 10/00 (2006.01)
C10L 5/00 (2006.01)
B03C 7/00 (2006.01)
(52) U.S. Cl. 44/602; 44/620; 252/88.1;
209/130
(58) Field of Classification Search 44/602,
44/620; 252/88,88.1; 209/130
See application file for complete search history.
(56) References Cited
U.S. PATENT DOCUMENTS
* cited by examiner
Primary Examiner---Cephia D. Toomer
(74) Attorney, Agent, or Firm-Sheridan Ross P.c.
The present invention discloses methods to reduce dusting in
bulk materials, such as coal. The method includes mixing
with the bulk material either a fraction of the bulk material
having an electrostatic charge opposite that ofthe remainder
of the bulk material or a heterologous charge control agent
having an electrostatic charge opposite that of the bulk
material. The attractive forces between the opposite electrostatic
charges agglomerate dust particles to larger particles
that quickly settle to control dusting. Also disclosed
are materials produced by the methods described above.
US 2003/0178598 Al Sep. 25, 2003
(57) ABSTRACT
2,139,398 A * 12/1938 Allen 44/600 9 Claims, 2 Drawing Sheets
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US 7,208,023 B2
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US 7,208,023 B2
2
BRIEF DESCRIPTION OF THE FIGURES OF
THE INVENTION
FIG. 1 is an illustration of a cup charging apparatus.
FIG. 2 is an illustration of a flat plate charging apparatus.
particles that quickly settle to control dusting. The present
invention is suitable for use with a wide variety of bulk
materials. For example, the bulk material can be a bulk fuel
material, such as coal, which can be selected from bituminous
coal, sub-bituminous coal, and lignite. In one preferred
embodiment, the first fraction is less than about 20% by
weight of the bulk material. In addition, the method can
include reducing the particle size of the first fraction to less
than about 2.0 mm before the step of imparting.
10
The step ofimparting can include placing the first fraction
in an electrostatic field of at least about I kV/cm and raising
the temperature of the first fraction in the electrostatic field
to between about 30° C. and about 300° C. Further, the first
15 fraction is then maintained in the electrostatic field and at the
raised temperature for between about 5 minutes and about
600 minutes. In another embodiment, the step of imparting
an electrostatic charge can include treating the first fraction
with a corona discharge.
In a preferred method of the present invention, a solid
particulate material is treated by separating it into first and
second fractions, wherein the first fraction is less than about
10% of the total material. The particle size of the first
fraction is reduced to about 0.5 mm and the first fraction is
25 placed in an electrostatic field ofat least about I kV/cm. The
temperature of the first fraction in the electrostatic field is
raised to between about 30° C. and about 300° c., and the
first fraction is maintained in the electrostatic field and at the
30 raised temperature for between about 5 minutes and about
600 minutes. The first fraction is then cooled to ambient
temperature while maintaining the electrostatic field, which
is removed when the material temperature is at ambient
temperature. The first and second fractions are then mixed.
In another embodiment of the present invention, dusting
in a bulk material having a first electrostatic charge is
controlled by mixing a heterologous charge control agent
with the bulk material. The heterologous charge control
agent has a second electrostatic charge opposite that of the
40 first electrostatic charge. Further, the amount of the heterologous
charge control agent is between about 0.1% and
about 20% by weight ofthe bulk material. The heterologous
charge control agent can be selected from toner, titanium
dioxide, coal, plaster of Paris, pitch coal blend, and sodium
45 orthophosphate.
In an alternative embodiment, the charge control agent
can be treated to impart the second electrostatic charge
opposite the first electrostatic charge. Such treatment can
include placing the charge control agent in an electrostatic
50 field of at least about I kV/cm, raising the temperature ofthe
charge control agent to between about 30° C. and about 300°
c., and maintaining the charge control agent in the electrostatic
field and at the raised temperature for between about
5 minutes and about 600 minutes. The charge control agent
55 can have either a net positive electrostatic charge or a net
negative electrostatic charge.
Further embodiments of the present invention include
bulk materials and particulate materials having the charac60
teristics ofmaterials produced by the various methods of the
present invention.
FIELD OF INVENTION
SUMMARY OF THE INVENTION
CROSS-REFERENCE TO RELATED
APPLICATION
BACKGROUND OF THE INVENTION
1
DRY DUST CONTROL MATERIALS
The present invention relates to methods of suppressing
dust produced by handling bulk materials such as coal, ore,
crushed rock, fertilizer, clay, grain and coke.
This application claims priority under 35 U.S.c. § 119(e)
from U.S. Provisional Application Ser. No. 60/357,540 filed
Feb. 15,2002, entitled "Dry Dust Control Materials," which
is incorporated herein by reference.
Producing, handling and storing bulk materials such as
coal, ore, crushed rock, fertilizer, clay, grain and coke 20
creates dust. Dust emissions add significant costs to mining,
handling, and storing bulk materials such as coal, aggregate,
and ore. Dust is noxious and can be dangerous ifthe material
is flammable. There are many examples of coal and grain
dust explosions that have taken lives and destroyed property.
Dust is easily carried by the wind, creating toxic or unsightly
conditions. Many handling operations have long recognized
the fugitive dust problems and have imposed strict controls
that can limit the capacity of a material handling facility.
Industry typically mitigates dust by applying water sprays
at transfer points to agglomerate the dust. Costly chemicals
such as foaming agents and surfactants may be added to the
water to increase effectiveness. Numerous patents have been
granted for specific dust suppression chemicals. For
example, U.S. Pat. No. 5,310,494 (Method for controlling 35
dusting of coke and coal, Bennett; Robert P., May 10, 1994)
teaches that a foaming agent consisting of polyacrylate and
lignosulfonate significantly reduces the amount of water
required to control fugitive dust.
Traditional dust suppression methods have limited effectiveness
for at least two reasons. First, dust created by
friction and impact after the application may not be effectively
controlled, so repeated applications may be required
at each transfer point in the material handling process.
Second, the water or chemical sprays evaporate, allowing
dust to become airborne.
Water and chemical sprays dilute or contaminate the bulk
material. For example, a small addition of I weight percent
addition of water to coal will reduce its useful heating value
by over 100 BTU/lb. Added water in cold weather creates
ice that causes costly material handling problems.
Therefore, there remains a need in the art for improved
methods of dust control that have greater effectiveness and
avoid the problems associated with water and chemical
sprays.
One embodiment of the present invention is a method to
control dusting in a bulk material wherein the bulk material
has a first electrostatic charge. The method includes separating
the bulk material into first and second fractions and
imparting a second electrostatic charge to the first fraction.
The second electrostatic charge is opposite the first electrostatic
charge. The first and second fractions are then mixed. 65
In this manner, the attractive forces between the opposite
electrostatic charges agglomerate dust particles to larger
US 7,208,023 B2
4
Limestone, for example, is particularly useful in cement
manufacture, road construction, rail ballast, soil amendment
or flue gas sorbent used in sulfur dioxide removal at coalfired
power plants.
Examples of bulk food products include, for example,
bulk grains, animal feed and related byproducts. The term
"bulk grains" include, for example, wheat, com, soybeans,
barley, oats and any other grain that are transported and/or
stored.
In one embodiment, the present invention is a method to
control dusting in a bulk material in which the bulk material
has a first electrostatic charge. The bulk material is separated
into first and second fractions and a second electrostatic
charge, opposite the first electrostatic charge, is imparted to
15 the first fraction. The electrostatic charge, i.e., the polarity of
the charge, of a material can be readily determined by those
skilled in the art, such as by use of a Faraday cup. Then the
first and second fractions are mixed. Because the treated first
fraction has a electrostatic charge opposite that of the bulk
20 material in the second fraction, any dust is immediately
attracted to the treated material and agglomerated. In this
embodiment, the first fraction is typically less than about
20% by weight of the total bulk material, more preferably
less than about 15%, and more preferably less than about
25 10%. In further embodiments, the particle size of the first
fraction can be reduced, such as by crushing or sorting to
less than about 2.0 mm before the step of imparting, more
preferably less than about 1.0 mm, more preferably less than
about 0.5 mm, and more preferably less than about 0.1 mm.
The step of imparting a second electrostatic charge to the
first fraction can be conducted in any manner known to those
of skill in the art. Field strength, temperature and time are
material and application specific and can be determined by
those skilled in the art in view of the disclosure herein. The
35 imposed electrostatic charge, opposite that of the bulk
material, remains for days, if not weeks, after the treated
material is cooled to ambient temperature. New dust generated
by friction and attrition after the initial application is
attracted to the treated material. Sufficient treated material is
40 produced to agglomerate the anticipated dust generated for
the life of the product. For example, the first fraction can be
placed in an electrostatic field of at least about I kV/cm, and
the temperature of the first fraction in the electrostatic field
raised to between about 30° C. and about 300° C. The first
45 fraction can be held under these conditions for a time
between about 5 minutes and about 600 minutes. The
material is then cooled to ambient temperature while maintaining
the electrostatic field, at which time the eletrostatic
field is disengaged. In another embodiment, the step of
50 imparting a second electrostatic charge to the first fraction
can be accomplished by treating the first fraction with a
corona discharge.
A particular embodiment of the present invention is a
method of treating a solid particulate material that includes
55 separating the material into first and second fractions, with
the first fraction being less than about 10% of the total
material and reducing the particle size of the first fraction to
less than about 0.5 mm. The first fraction is then placed in
an electrostatic field of about I kV/cm or more and the
60 temperature of the first fraction in the electrostatic field is
raised to between about 30° C. and about 300° C. The first
fraction is maintained under these conditions for between
about 5 minutes and about 600 minutes before being cooled
to ambient temperature while maintaining the electrostatic
65 field. Then the first fraction is removed from the electrostatic
field when the material temperature is at ambient temperature
and mixed with the second fraction.
3
DETAILED DESCRIPTION OF INVENTION
A novel method of dust control is described herein that
avoids the problems described above with conventional dust
control methods. The invention imparts electrostatic charges
to a portion of the bulk material or to a heterologous charge
control agent and the resulting attractive forces agglomerate
dust particles to larger particles that quickly settle. The
invention has a number of attendant advantages. The resultant
mixture possesses less dust than untreated material 10
without further treatment until the material is moved to
market and consumed. The electrostatic charges remain
effective from the point of application to the end use of the
bulk material and therefore subsequent treatment of dust
control is reduced or avoided altogether. In addition, when
a portion of the bulk material is used, no change in the
composition of the bulk material occurs during implementation
ofthe invention. Compared to present methods of dust
control, the present method is lower cost, and provides a
more durable treatment, greater overall effectiveness, and
preservation of product quality.
Undesirable and excessive dust problems occur because
electrostatic charges are normally produced when a bulk
material, such as coal, is moved on conveyors and past bins
and hoppers. Most particles, including dust, take on the same
net electrostatic charge during handling, and since particles
oflike electrostatic charge repulse each other, dispersing the
dust particles. The present invention overcomes the natural
tendency for materials to disperse dust by imparting an
electrostatic charge, opposite that of the natural electrostatic 30
charge of the bulk material, to a portion of the bulk material
As used herein, the term "dusting" refers to the phenomenon
of small particulate matter in a bulk material becoming
airborne during production, handling or storage of the bulk
material.
As used herein, the term "bulk material" refers to any
solid materials that are produced, shipped and/or stored in
quantities that are generally measured on a tonnage basis
and that can be fractionated or separated by size. Bulk
materials can include, for example, solid fuel materials, bulk
food products, sulfide ores, carbon-containing materials,
such as activated carbon and carbon black, and other minerals
and ores.
As used herein, the term "solid or bulk fuel material"
generally refers to any solid material that is combusted or
otherwise consumed for a useful purpose. More particularly,
solid fuel materials can include, for example, coal, upgraded
coal products, and other solid fuels, including coke and other
thermally treated fuel material. The term "coal" as used
herein includes anthracite, bituminous coal, sub-bituminous
coal and lignite. The present invention is particularly suited
for bituminous coal, sub-bituminous coal and lignite. The
term "upgraded coal products" includes thermally upgraded
coal products, coal products produced by beneficiation
based on specific gravity separation, mechanically cleaned
coal products, and coal products such as stoker, breeze, slack
and fines.
Examples of other solid fuels included, without limitation,
oil shale, solid biomass materials, refuse derived fuels
(including municipal and reclaimed refuse), coke, char,
petroleum coke, gilsonite, distillation byproducts, wood
byproducts and their waste, shredded tires, peat and waste
pond coal fines. The term "refuse derived fuels" can include,
for example, landfill material from which non-combustible
materials have been removed. Examples of ores and minerals
that are mined include, without limitation, ores (such as
sulfide ores), gravel, rocks, crushed rocks and limestone.
US 7,208,023 B2
5 6
Screen Aperture
Tyler Screen Mesh Direct Values
Passing Retained Weight, g Weight, %
40
6 0.0 0.0
6 14 129.4 33.5
14 28 131.0 33.9
28 48 65.4 16.9
48 100 33.5 8.7
100 Pan 27.3 7.1
Value
27.08
5.43
0.32
8,851
TABLE I
TABLE 3
TABLE 2
Description
Photocopier Toner
Dupont, TI-PURE
Coal-fired Power Plant
Coal-fired Power Plant
Screenings, Raw Untreated
Screenings, Charged at 20 kV, 40 c c.,
15 min in Cup Apparatus
Raw Powder
Raw Powder, Charged at 27 kV, 20 c c.,
15 min in Cup Apparatus
Minus 30 Mesh
Minus 30 Mesh, Charged at 9 kV, 20c c.,
1 hr in Flat Plate Apparatus
Dry Dust Control Agents
Particle Size Distribution (Dry Screen)
Parameter
Moisture, %
Ash, %
Sulfur, %
Higher Heating Value,
Btu/lb
Analysis of PRE Coal Used in Tests (As-received Basis)
Dust Control Agents.
Eight dry, finely powdered materials were tested as dust
control agents. Table 3 lists the materials used in the tests.
Equipment.
The experiments described below used a top loading
balance, pans, riffle splitter, two fabricated charging devices
and an optical static dust tester. One of the charging devices,
a cup charge apparatus, is shown in FIG. 1 and the other, a
flat plate charge apparatus, is shown in FIG. 2. The two
charging devices were powered with a Bertran Model 935
high-voltage power supply (0 to 30 kV DC)
Pitch Coal Blend
65 Pitch Coal Blend (Treated)
Toner
Titanium Dioxide
Type C Fly Ash
Type F Fly Ash
60 28- by 48-mesh PRB Coal
28- by 48-mesh PRB Coal
(Treated)
Plaster of Paris
Plaster of Paris (Treated)
10 Materials.
Coal Sample.
A fresh sample of 3-inch by 0 subbituminous coal
obtained from a mine in the southern PRB was used for the
tests. An analysis ofthe sample is listed in Table I. Approximate
y 5 kg of sample was partially dried at 50° C. for I hr
to remove visible surface moisture, crushed in a hammer
mill to minus 8 mesh, and riffled into 200-g lots. The 200-g
lots were sealed in plastic bags for use. The particle size
distribution of the minus 8-mesh lots was obtained by dry
screen analysis. Results are listed in Table 2.
55 Material
EXAMPLES
Thirty-one experiments were conducted to evaluate various
methods of the present invention in the mitigation of
dust produced by samples of Powder River Basin (PRB)
subbituminous coal.
In another embodiment of the present invention, a method
to control dusting in a bulk material having a first electrostatic
charge is provided. The method includes mixing a
heterologous charge control agent with the bulk material,
wherein the heterologous charge control agent has a second
electrostatic charge opposite that of the first electrostatic
charge. Typically, the amount of the heterologous charge
control agent is between about 0.1% and about 20% by
weight of the bulk material.
The heterologous charge control agent is a material having
a different chemical makeup than the bulk material.
Another characteristic of a charge control agent is that it has
an electrostatic charge opposite that of the electrostatic
charge of the bulk material. Thus, the charge control agent 15
can have a net positive or negative electrostatic charge,
depending on the charge of the bulk material. For example,
the charge control agent can have a static electrical charge
produced by frictional forces from mixing that impart static
charges, this phenomena is referred to as a triboelectric 20
charging. Alternatively, the charge control agent can possess
a durable electrostatic charge that is stronger than charges
produced by mixing. Materials that possess permanent,
durable static charges are called electrets. Electrets are
manufactured materials that gain electrical charges by an 25
intense electrical field or a corona discharge. Analogous to
permanent magnets, electrets are routinely used in xerographic
toners, electrostatic filters, and other electronic
devices. Electrets tested as dust suppression agents include
xerographic toner powder and materials charged in a strong 30
electrostatic field. In preferred embodiments, the heterologous
charge control agent can be toner, titanium dioxide,
coal, plaster of Paris, pitch coal blend, or sodium orthophosphate.
In a particular embodiment, the heterologous charge con- 35
trol agent can be mixed first with only a portion of the bulk
material with the resulting mixture then being mixed with
the remaining portion of the bulk material. In this manner,
the charge control agent can be more evenly and uniformly
mixed throughout the bulk material. For example, the charge
control agent can be mixed with a first portion of the bulk
material that is between about 0.5% and about 25% of the
bulk material. This mixture is then mixed with the remaining
portion of the bulk material.
The dust suppression effect of the treatment of materials 45
in accordance with the methods of the present invention is
durable. In preferred embodiments, the suppression effect
continues for at least about 50 hours after initial treatment,
more preferably at least about 100 hours, more preferably at
least about 200 hours and more preferably at least about 300 50
hours.
Further embodiments of the present invention include
bulk materials and solid particulate materials having the
characteristics of the materials produced by methods of the
present invention described herein, including the materials
produced by such methods.
The following examples are provided for purposes of
illustration and are not intended to limit the scope of the
present invention.
US 7,208,023 B2
7 8
light transmission values at 15, 30, 60, 120, and 300 seconds.
Extend the period to 600 seconds if the sample is dusty
and the transmission is less than 90% at 300 seconds.
5. At the conclusion of the test, empty and clean the dust
apparatus. Place the spent sample in a bag for archival
purposes.
Results.
Thirty-one tests were conducted with PRB coal and eight
10 types of dust control agents. Results for all tests conducted
are listed in Table 4.
Results for dust suppression agents that were not treated
in the cup or flat plate apparatus were compared with
untreated raw coal. Results are summarized in Table 5.
Selected dust control agents were treated in an electrostatic
field in the cup charging apparatus or flat plate
apparatus. Treated plaster of Paris, pitch coal, and sodium
orthophosphate mitigated dust more effectively than
20 untreated materials, as listed in Table 6. These three materials
contain water molecules that may have been polarized
by the intense electric field.
Minus 14-mesh Crystals
Minus 14-mesh Crystals, Charged at 20 kY,
20c C, 15 min in Cup Apparatus
Description
Dry Dust Control Agents
TABLE 3-continued
Material
Procedures.
The following five-step procedure was used to prepare
and measure the dustiness of each coal sample:
1. Weigh out 200 g of the minus 8-mesh coal sample in a
15 pan.
2. Weigh out the specified weight of dust control agent.
3. Combine the coal and dust control agent and pass the
materials through a riffle splitter five times to homogenize
the mixture.
4. Place the homogenized mixture in the optical static dust
tester feed hopper and conduct the dustiness test. Record the
Na3P04012H20
Na3P04012H20 (Treated)
TABLE 4
Dustiness Test Results
Treatment
Concentration Treatment Charging
Light Transmittance, %
(seconds)
Run Sample Weight % Treatment Method 15 30 60 120 300 600
8-mesh
Fresh PRE
2 8-mesh
Fresh PRE
8-mesh
Fresh PRE
4 8-mesh
Fresh PRE
8-mesh
Fresh PRE
8-mesh
Fresh PRE
7 8-mesh
Fresh PRE
8-mesh
Fresh PRE
9 8-mesh
Fresh PRE
10 Run 9
11 Run 10
12 Run 11
13 8-mesh
Fresh PRE
14 8-mesh
Fresh PRE
15 8-mesh
Fresh PRE
16 8-mesh
Fresh PRE
17 8-mesh
Fresh PRE
18 8-mesh
Fresh PRE
19 8-mesh
Fresh PRE
20 8-mesh
Fresh PRE
21 8-mesh
Fresh PRE
22 8-mesh
Fresh PRE
23 8-mesh
Fresh PRE
a
a
a
a
a
10
17
17
17
a
None, Direct from
Sample Bag
None, Direct from
Sample Bag
None, Direct from
Sample Bag
None, Direct from
Sample Bag
None, Direct from
Sample Bag
Photocopier
Toner
Photocopier
Toner
Photocopier
Toner
Run 8 Sample,
20 hr Later
312 hr Later
Dried 50C C, 6%
Moisture Loss
Tumbled 15 min
Photocopier
Toner
PRE,
48 by 200 Mesh
PRE,
48 by 200 Mesh
PRE,
48 by 200 Mesh
None,
Riffled 5 Times
Titania
Type C Fly Ash
Type F Fly Ash
Treated Plaster of
Paris, 27 kY
As-received
Plaster of Paris
Coal Pitch
None 41 52 66 81 >100
None 49 58 67 78 95 100
None 50 58 67 77 91 95
None 30 36 44 72 72 75
None 49 59 68 78 94 99
None 82 86 90 92 92 93
None 92 96 97 98 98
None 87 92 97 98
None 89 92 95 96.6 99
None 88 94 97 99 100
None 89 92 95 98 99 100
None 65 74 84 93 96 98
25 kY, 1 min, 20 C C, 89 92 96 98 100
cup apparatus
20 kY, 15 min, 40C C, 66 74 82 89 95 97
cup apparatus
None 75 84 88 94 98
None 77 84 88 94 98
None 52 61 71 78 92
None 78 84 89 94 97
None 46 55 64 74 93 95
None 55 64 73 82 93 96
27 kY, 15 min, 20C C, 70 78 84 89 98
cup apparatus
None 53 62 70 80 99
None 54 64 76 82 97
US 7,208,023 B2
9 10
TABLE 4-continued
Dustiness Test Results
Treatment Light Transmittance, %
Concentration Treatment Charging (seconds)
Run Sample Weight % Treatment Method 15 30 60 120 300 600
24 8-mesh Coal Pitch 9 kV/inch, 15 min, 66 73 80 85 94 96
Fresh PRE 20 c c., flat plate
apparatus
25 8-mesh 0 Dried 1 hr, 50c C. None 47 61 69 81 91 97
Fresh PRE
26 Run 22 0 Tumbled 15 min None 27 38 52 65 87 93
27 Run 23 1 Added None 81 88 94 97 99 100
Photocopier
Toner
28 8-mesh Raw None 55 65 75 83 92 96
Fresh PRE Na3P04012H20
29 8-mesh Raw 20 kV, 15 min, 20C c., 64 76 82 87 95 98
Fresh PRE Na3P04012H20 cup apparatus
30 8-mesh 0.3 0.67 g Cling-free None 48 57 67 75 90 98
Fresh PRE Cloth, Tumbled
31 8-mesh 0.3 0.53 g Grab It None 57 66 73 82 94 98
Fresh PRE Cloth, Tumbled
Dust Suppression Agents Treated by Electrostatic Field
Test Result Summary for Non-Treated Dust Suppression Agents
TABLE 6
TABLE 5
What is claimed:
1. A method to control dusting in a bulk material having
65 a first electrostatic charge, comprising:
separating the bulk material into a first and second fraction;
25 Conclusions.
The foregoing experimental results support the following
conclusions.
1. Electrostatic attraction between the dust control agent
30 and coal dust is the cause of dust suppression.
2. Dust control with toner was effective after 13 days. In
addition, significant control was observed after the sample
was dried (6% moisture loss) and tumbled in a mill for 15
mill.
3. Commercial electret (photocopier toner) was more
effective than electrets produced by the cup or flat plate
charging devices.
4. Dustiness is highly dependent on particle size distribution,
in particular to the concentration ofminus 1DO-mesh
40 particles.
5. Untreated titanium dioxide at a 1% concentration is
moderately effective.
6. Treated agents, including plaster of Paris, pitch coal,
and sodium orthophosphate, were more effective than their
45 untreated counterparts.
The foregoing description of the present invention has
been presented for purposes of illustration and description.
Furthennore, the description is not intended to limit the
invention to the form disclosed herein. Consequently, varia-
50 tions and modifications commensurate with the above teachings,
and the skill or knowledge of the relevant art, are
within the scope of the present invention. The embodiment
described hereinabove is further intended to explain the best
mode known for practicing the invention and to enable
55 others skilled in the art to utilize the invention in such, or
other, embodiments and with various modifications required
by the particular applications or uses of the present invention.
It is intended that the appended claims be construed to
include alternative embodiments to the extent pennitted by
60 the prior art.
35
Dustiness, Change
Light Transmittance Compared to
at 60 sec, %1 Untreated Coal at 60 sec2
Dustiness, Change
Compared to
Untreated Agent at 1%
Electrostatic Treatment Concentration (60 sec) 1
Cup Apparatus, 25 kV, No Change
1 min, 20 C C.
Cup Apparatus, 20 kV, No Change
15 min, 40C C.
Cup Apparatus, 27 kV, 20% Decrease
15 min, 20C C.
Flat Plate Apparatus, 9 5% Decrease
kV/inch, 15 min, 20 C C.
Cup Apparatus, 20 kV, 9% Decrease
15 min 20 C C.
lUntreated raw coal light transmittance was 68% at 60 sec. Less than 5%
change after treatment was indicated as no change.
Dust Suppression Agent
and Concentration
Pitch Coal
Toner, 10% 90 32% Decrease
Toner, 5% 97 42% Decrease
Toner, 1% 95 40% Decrease
Type C Fly Ash, 1% 64 No Change
Type F Fly Ash, 1% 73 7% Decrease
TI-PURE Ti02, 1% 89 31% Decrease
Plaster of Paris, 1% 70 No Change
Pitch Coal, 1% 76 12% Decrease
Na3P04012H20,1% 75 10% Decrease
Toner
1Higher value indicates less dust.
2Untreated raw coal light transmittance was 68% at 60 sec. Less than 5%
change after treatment was indicated as no change.
Dust Suppression
Agent
48- by 200-mesh
PRB Coal
Plaster of Paris
Na3P04012H20
11
US 7,208,023 B2
12
imparting a second electrostatic charge to the first fraction,
wherein the second electrostatic charge is opposite
the first electrostatic charge; and
mixing the first and second fractions.
2. The method, as claimed in claim 1, wherein the first
fraction is less than about 20% by weight of the total bulk
material.
3. The method, as claimed in claim 1, further comprising
reducing the particle size of the first fraction before the step
of imparting. 10
4. The method, as claimed in claim 1, wherein the step of
imparting comprises,
placing the first fraction in an electrostatic field of at least
about I kV/cm;
raising the temperature of the first fraction in the electro- 15
static field to between about 30° C. and about 300° c.;
and
maintaining the first fraction in the electrostatic field and
at the raised temperature for between about 5 minutes
and about 600 minutes. 20
5. The method, as claimed in claim 1, wherein the step of
imparting comprises treating the first fraction with a corona
discharge.
6. The method, as claimed in claim 1, wherein the bulk
material is a bulk fuel material. 25
7. The method, as claimed in claim 1, wherein the bulk
material is coal selected from the group consisting of
bituminous coal, subbituminous coal and lignite.
8. A method of treating a solid particulate material,
comprising: 30
a. separating the material into first and second fractions,
wherein the first fraction comprises less than about
10% of the total material;
b. reducing the particle size of the first fraction;
c. placing the first fraction in an electrostatic field of at
least about I kV/cm;
d. raising the temperature of the first fraction in the
electrostatic field to between about 30° C. and about
300° c.;
e. maintaining the first fraction in the electrostatic field
and at the raised temperature for between about 5
minutes and about 600 minutes;
f. cooling the first fraction to ambient temperature while
maintaining the electrostatic field;
g. removing the first fraction from the electrostatic field
when the material temperature is at ambient temperature;
and
h. mixing the first and second fractions.
9. A method to control dusting in a bulk material having
a first electrostatic charge, comprising:
placing a charge control agent in an electrostatic field of
at least about I kV/cm;
raising the temperature of the charge control agent in the
electrostatic field to between about 30° C. and about
300° c.;
maintaining the charge control agent in the electrostatic
field and at the raised temperature for between about 5
minutes and about 600 minutes; and,
mixing the bulk material with a charge control agent
having a second electrostatic charge opposite the first
electrostatic charge, wherein the amount of the charge
control agent is between about 0.1% and about 20% by
weight of the bulk material.
* * * * *
fam�� H�^D��OCR'>a) providing a feed stream comprising an elemental
sulfur-bearing material and a dispersant wherein said
dispersant comprises at least one of a surfactant,
ground sand, mineral processing tailings, or combination
thereof, and wherein said elemental sulfur-bearing 25
material comprises an elemental sulfur-containing residue
from a pressure leaching operation carried out at a
temperature in the range of about 1400 C. to about 1800
c.;
b) pressure leaching at least a portion of said feed stream 30
at a temperature in the range of about 2200 C. to about
275 0 C. in an oxygen-containing atmosphere in an
agitated multiple-compartment pressure leaching vessel
to form a product slurry comprising a sulfuric acid
solution;
c) separating at least a portion of said sulfuric acid 35
solution from said product slurry to yield a residue;
d) recovering at least one metal value from said residue.
2. The process of claim 1 wherein said step of recovering
at least one metal value from said residue comprises recovering
at least one precious metal from said residue.
3. The process of claim 1 wherein said step of pressure
leaching at least a portion of said feed stream comprises
pressure leaching at temperatures above about 2350 C.
4. A treatment process comprising the steps of:
a) providing a feed stream comprising an elemental 45
sulfur-bearing material-wherein said elemental sulfurbearing
material comprises an elemental sulfur-containing
residue from a pressure leaching operation
carried out at a temperature in the range of about 1400
C. to about 1800 c.; 50
b) pressure leaching at least a portion of said feed stream
in the presence of a dispersant wherein said dispersant
comprises at least one of a surfactant, ground sand,
mineral processing tailings, or combination thereof, at
a temperature in the range of about 2200 C. to about
275 0 C. in an oxygen-containing atmosphere in an 55
agitated multiple-compartment pressure leaching vessel
to form a product slurry comprising a sulfuric acid
solution;
c) separating at least a portion of said sulfuric acid
solution from said product slurry to yield a residue;
d) recovering at least one metal value from said residue.
5. The process of claim 4 wherein said step of recovering
at least one metal value from said residue comprises recovering
at least one precious metal from said residue.
6. A process for recovering metal values from an elemental
sulfur-bearing solid residue of a pressure leaching pro
='fo�`�ie�^D��nt-family:"Times New Roman","serif";mso-fareast-font-family: HiddenHorzOCR'>at a temperature in the range of about 220° C. to
about 275° C. in an oxygen-containing atmosphere in
an, agitated multiple-compartment pressure leaching
vessel to form a product slurry comprising a sulfuric
acid solution;
c) adding a dispersant during said pressure leaching step;
d) separating at least a portion of said sulfuric acid
solution from said product slurry to yield a solid
residue;
e) recovering at least one precious metal value from said
solid residue.
17. The process of claim 16 wherein said step of providing
an elemental sulfur-bearing material comprises providing an
5 elemental sulfur-containing residue from a pressure leaching
operation carried out at a temperature in the range of about
140° C. to about 180° C.
18. The process of claim 16 wherein said step of pressure
10 leaching comprises pressure leaching at a temperature of
about 235° C.
* * * * *