111111111111111111111111111111111111111111111111111111111111111111111111111
US00678694lB2
(12) United States Patent
Reeves et al.
(10) Patent No.:
(45) Date of Patent:
US 6,786,941 B2
Sep.7,2004
(73) Assignee: Hazen Research, Inc., Golden, CO
(US)
(54) METHODS OF CONTROLLING THE
DENSITY AND THERMAL PROPERTIES OF
BULK MATERIALS
(75) Inventors: Robert A. Reeves, Arvada, CO (US);
Charlie W. Kenney, Littleton, CO
(US); Mark H. Berggren, Golden, CO
(US)
(List continued on next page.)
FOREIGN PATENT DOCUMENTS
.............. 241/24.31
.............. 241/24.31
C06D/5/oo
Burstlein 75/750
Ellman 34/9
Roberts et al. 241/22
Cummings 501/109
Hildebrandt 241/20
Karpinski et al. 241/24
Lohrmann .. 44/503
Verschuur 44/10 E
Stewart ... 106/56
Trumbull et al. 414/808
7/1973
10/1976
* 2/1990
6/1965
4/1966
10/1967
* 12/1968
1/1969
10/1975
1/1976
5/1976
7/1976
8/1977
2335042
2513366
3827397
3,189,436 A *
3,243,889 A
3,346,198 A
3,415,667 A
3,421,991 A
3,912,174 A
3,933,443 A *
3,957,456 A
3,969,124 A
4,044,904 A *
DE
DE
DE
Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 11 days.
( *) Notice:
(21) Appl. No.: 10/197,454
(22) Filed: Jul. 16,2002
(65) Prior Publication Data
us 2003/0132326 A1 Jul. 17,2003
U.S. PATENT DOCUMENTS
References Cited
Related U.S. Application Data
ABSTRACT
OTHER PUBLICATIONS
Methods of controlling the bulk density, permeability, moisture
retention and thermal properties of bulk materials are
provided by selectively sizing the bulk material. Preferably,
the bulk material is sized into successively smaller particle
size fractions, with the largest fraction placed into a confined
area. The next smaller size fraction is then added until the
largest sized fraction begins to dilate. The next successive
smaller size fraction is added until the mixture beams to
dilate, with the process being continued until the smallest
size fraction is used. Methods of decreasing the density of
bulk materials are also provided.
4 Claims, 8 Drawing Sheets
(57)
Furnas, c.c.; "Grading Aggregates"; Industrial and Engineering
Chemistry; vol. 23, No.9; Sep. 1981; pp.
1052-1058.*
(List continued on next page.)
Primary Examiner-Donald R Walsh
Assistant Examiner-Daniel K Schlak
(74) Attorney, Agent, or Firm---8heridan Ross Pc.
2/1910 Rodman 106/285
8/1936 Marquard .. 241/81
6/1940 Watties 44/541
1/1956 Weston 241/81
8/1964 Johnson 241/22
5/1965 Noren et al. 241/22
Division of application No. 09/608,722, filed on Jun. 30,
2000, now Pat. No. 6,422,494.
Int. CI? . COIL 5/00; B07B 15/10
U.S. Cl. 44/503; 44/592; 44/620;
209/10
Field of Search 241/81,24.31;
44/503, 592, 595, 608, 520; 209/10
949,445 A *
2,049,814 A
2,204,781 A *
2,729,397 A
3,145,644 A
3,181,800 A
(62)
(51)
(52)
(58)
(56)
2·lncllllOF!ed
xl/a'inch
ltaxi/llul/ldtn5lty2- .O-lllcl\fina\ Product
US 6,786,941 B2
Page 2
U.S. PATENT DOCUMENTS
4,078,902 A * 3/1978 Olson 44/559
4,083,940 A 4/1978 Das 423/449
4,156,595 A * 5/1979 Scott et al. 44/578
4,170,456 A 10/1979 Smith 44/1 F
4,186,054 A 1/1980 Brayton et al. . 201/6
4,188,231 A * 2/1980 Valore 106/700
4,190,422 A * 2/1980 Hitzrot, Jr. 51/309
4,231,978 A * 11/1980 Crookston 264/660
4,244,813 A * 1/1981 Moyer, Jr. . 209/5
4,257,848 A 3/1981 Brayton et al. 202/82
4,299,205 A * 11/1981 Garfield 126/674
4,304,636 A 12/1981 Kestner et al. 201/20
4,396,394 A 8/1983 Li et al. . 44/1 G
4,401,436 A 8/1983 Bonnecaze 44/1 G
4,403,996 A * 9/1983 Matsuura et al. 44/502
4,450,046 A 5/1984 Rice et al. 201/20
4,498,523 A * 2/1985 Bowman et al. 164/477
4,511,363 A 4/1985 Nakamura et al. 44/1 G
4,599,250 A 7/1986 Cargle et al. 427/320
4,613,429 A 9/1986 Chiang et al. 209/5
4,650,495 A 3/1987 Yan 44/1 G
4,662,894 A * 5/1987 Greenwald, Sr. .. 44/280
4,759,772 A 7/1988 Rogers et al. 44/501
4,778,482 A 10/1988 Bixel et al. 44/501
4,784,333 A 11/1988 Hikake et al. 241/81
4,797,136 A 1/1989 Siddoway et al. 44/501
4,828,575 A 5/1989 Bellow, Jr. et al. 44/501
4,828,576 A 5/1989 Bixel et al. 44/501
4,863,317 A * 9/1989 Boyle 406/109
4,957,596 A 9/1990 Ukita et al. 201/20
5,022,317 A * 6/1991 Williams 100/35
RE33,788 E 1/1992 Clay 149/1
5,087,269 A 2/1992 Cha et al. 44/626
5,124,162 A 6/1992 Boskovicet al. 426/96
5,263,650 A 11/1993 Yasui et al. 241/22
5,314,124 A 5/1994 Kindig 241/20
5,338,573 A * 8/1994 Davies et al. 427/331
5,435,813 A 7/1995 Evans 44/620
5,545,796 A * 8/1996 Roy et al. 588/4
5,609,458 A 3/1997 Hanaoka et al. 414/173
5,725,613 A 3/1998 Reeves et al. 44/501
5,795,484 A * 8/1998 Greenwald, Sr 210/696
5,795,856 A 8/1998 Hatano et al. 510/444
5,819,945 A 10/1998 Laskowski et al. 209/2
5,919,277 A 7/1999 Reeves et al. 44/501
5,968,891 A 10/1999 Mallari et al. 510/444
6,083,286 A * 7/2000 Ono 44/280
6,085,912 A * 7/2000 Hacking et al. 209/17
6,126,705 A * 10/2000 Pryor et al. 44/607
6,231,627 B1 5/2001 Reeves et al. 44/620
6,395,662 B1 * 5/2002 Li et al. 501/127
6,524,354 B2 * 2/2003 Sinha et al. 44/564
OTHER PUBLICATIONS
Translation of German Patent 2,335,042-Published Jan.
30, 1975-lnventor: Rosslyn Mitchell. *
Edwards, J.H.; "Potential sources of CO2 and the options for
its large-scale utilization now and in the future"; Catalysis
Today, 1995; 23 pp. 59-66.
Keirn, Willi; "Industrial Uses of Carbon Dioxide"; in Carbon
Dioxide as a Source of Carbon; M. Aresta and G. Forti,
eds.; D. Reidel Publishing Co.; 1987; pp. 23-31.
Rigsby et aI., "Coal self-heating: problems and solutions",
pp. 102-106 British Mentine Technils or Procedings of 2nd
Int'l coal Transportation and Headling conference.
Riley et aI., "Use of Carbon Dioxide to Reduce Self-Heating
in Barged Coal"; Journal of Coal Quality, Apr. 1987, pp.
64-67.
Ripp, John; "Understanding coal pile hydrology can help
BTU loss in stored coal"; pp. 146-150 10-1983 International
coal testing reference.
Sapienze et aI., "Carbon DioxidelWater for Coal Beneficiation";
in Mineral Matter and Ash in Coal; 1986; American
Chemical Society; pp. 500-512.
Furnas, c.c.; Flow of Gases Through Beds of Broken
Solids; Bulletin 307; United States Department of Commerce,
Bureau of Mines; United States Government Printing
Office; 1989; pp. 74-83.
Standish et aI., "Optimization of Coal Grind for Maximum
Bulk Density," Powder Technology, vol. 68, 1991, pp.
175-186.
* cited by examiner
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US 6,786,941 B2
1
METHODS OF CONTROLLING THE
DENSITY AND THERMAL PROPERTIES OF
BULK MATERIALS
The present application is a divisional of u.s. patent
application Ser. No. 09/608,722, filed Jun. 30, 2000, which
is incorporated herein by reference in its entirety (now U.S.
Pat. No. 6,422,494, issued Jul. 23, 2002.)
FIELD OF THE INVENTION
The present invention relates to methods of controlling
the density, permeability, moisture retention and thermal
properties of bulk materials and to compositions produced
by the methods.
BACKGROUND OF THE INVENTION
Efficient, low cost transportation and storage of bulk
materials from mines and/or factories to markets are vital to
certain industries because the costs of transporting and
storing bulk material are often major components of the total
cost of the delivered product.
Coal is one of the world's largest bulk commodities
moved by rail, truck, inland barges and ocean-going vessels
to utilities and steel mills. The cost of transporting coal plays
a critical role in expanding markets for coal. Changes in
environmental laws in the United States have created a
demand for low-sulfur, premium quality steam coal. Before
1975, underground mines in West Virginia and eastern
Kentucky supplied most of the premium quality coal needed
to meet environmental requirements at coal-fired utilities.
Although vast low-cost, strippable reserves of low sulfur
coal resided in the West, distance and associated high
transportation costs excluded them from serious consideration
for Midwestern and Eastern markets. This situation
changed as railroads recognized the opportunity for new
markets and began investing in unit trains and improved
ways and structures to haul large tonnage shipments. As a
result, large productive mines were developed in the Powder
River Basin (PRB) in Wyoming. Production of PRB coal has
risen steadily since 1980 replacing higher cost eastern coal.
Production is expected to rise to 400 million tons per year in
the near future. Since transportation can account for up to
75% of the total delivered price, it continues to play the
critical role in expanding the market for western coal. The
increased demand for PRB and other western coal will not
be realized unless the railroad companies continue to find
ways to reduce costs and improve efficiency.
The market for metallurgical coal is also dependent on the
cost of transportation. For example, steel mills are extremely
competitive and are constantly looking for lower cost coal to
fuel their blast furnaces. Although the best quality metallurgical
coal in the world reside in the eastern United States,
Australian and South African producers often win contracts
because of lower costs. The high cost of transporting coal by
rail from eastern mines to port facilities often makes American
suppliers non-competitive.
Coal has a low bulk density compared to many other
common bulk materials, such as limestone, aggregates, iron
ore and fertilizers. Since coal is hauled in the same rail cars,
trucks, barges and ocean-going vessels as the more dense
bulk materials, less weight can be carried for a given volume
of cargo hold. The full weight carrying capacity of many
vessels cannot be reached before the volumetric capacity is
reached. As a result, costs are increased since the weight
capacity of the vessel is underutilized. Consequently, a coal
producer is penalized because a rail car cannot be loaded to
2
full weight carrying capacity. One PRB mine operator
reported that underweight penalties cost about $100,000 per
month, totaling over $1 million ina recent year.
Storage and handling costs are also affected by bulk
5 density similar to transportation costs. As bulk density
increases, less storage volume is required to hold the same
amount of coal. Smaller stockpiles require less area to hold
coal resulting in lower storage costs. Likewise, the smaller
volume also requires less loading and unloading time and
10 labor.
When bulk materials are hauled in conveyances such as
rail car, barges, and trucks during cold weather, moisture
contained in the material may form ice that can adhere to the
conveyance. Frozen material, accounting for up to 10 per-
15 cent of the net payload, may not discharge from the conveyance
at the point of delivery. The added weight increases
transportation costs by reducing the useful carrying capacity
of the conveyance and increasing the weight of the conveyance
returned to the producer.
20
Sub-zero temperatures and long transit times can cause
the payload to freeze creating large lumps of aggregated
material, particularly when water goes through the material
and pools at the bottom of the conveyance before freezing.
25 As a result, special equipment is required to break the frozen
lumps into manageable sizes that are compatible with material
handling and storage equipment.
Two principal methods are typically used to mitigate the
adverse effects of frozen material. The first method involves
30 adding a chemical such as a salt compound or liquid glycol
antifreeze to the bulk material to depress the freezing point
of water or weaken the ice that binds the solid particles
together as described, for example, in U.S. Pat. No. 5,079,
036 entitled "Method of Inhibiting Freezing and Improving
35 Flow and Handleability Characteristics of Solid, Particulate
Materials" and in U.S. Pat. No. 4,290,810 entitled "Method
for Facilitating Transportation of Particulate on a Conveyor
Belt in a Cold Environment." The second principal method
involves heating the walls of the conveyance to thaw the
40 frozen layer of material adhering to the walls as described,
for example, in U.S. Pat. No. 4,585,178 entitled "Coal Car
Thawing System" and in U.S. Pat. No. 4,221,521 entitled
"Apparatus for Loosening Frozen Coal in Hopper Cars."
Several manufacturers offer electric and gas-fired radiant
45 heaters to warm the bottom and sides of a conveyance to
melt the frozen layer of material. The choices of chemical or
thermal methods depend on the type of conveyance, cost
constraints, and material compatibility. Treating frozen
materials has become more expensive because many rail
50 cars are fabricated from aluminum, a thermally sensitive
material that can corrode when it comes in contact with
low-cost salt compounds.
Thawing and chemical treatment methods are time consuming
and expensive. Thawing costs range between $0.20
55 and $0.50 per ton, depending on the source of energy.
Chemical treatment costs range between $0.20 and $1.00 per
ton, depending on the type of chemical and dose rate.
Most bulk materials that are crushed to a specified topsize
for commercial reasons have a naturally occurring particle
60 size distribution that, when plotted, fit under a typical single
gaussian curve. Such naturally occurring size distribution
does not have the optimum particle size distribution to
produce sufficiently high bulk densities to effectively lower
transportation and storage costs or to mitigate the effects of
65 freezing. In addition, known methods of altering the thermal
properties of bulk materials, such as lowering permeability
and increasing moisture retention, result in decreasing the
US 6,786,941 B2
3 4
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart of the method of increasing the
density of bulk materials by combining two particle size
fractions.
FIG. 2 is a flowchart of the method of increasing the
density of bulk materials by combining successively smaller
fractions to form a composition of multiple sized particles.
FIG. 3 is a void-filling depiction of a multiple size fraction
composition having a density of 115% of normal and a void
space of 28%.
25
occupy the void between the coarse particles to achieve the
highest bulk density. Accordingly, the present invention is
based, in part, on the discovery that mid-sized particles
impede the flow of the fine particles in filling this void,
which results in lower bulk density.
In alternative methods for increasing the density of a bulk
material, the bulk material is first fractionated into increasingly
smaller particle fractions. The largest particle size
fraction is placed into a holding area or compartment. The
next smaller fraction is then added to fill the void between
the larger particles. Filling is continued until the smaller
particles begin to dilate the entire mixture (i.e., push the
larger particles apart) thus reducing bulk density. At that
point, the next smaller size fraction is added filling the void
until the entire mixture begins to dilate. This process is
continued with each successive smaller size fraction.
Although the methods of this embodiment may require more
processing steps than the first embodiment, it can be used to
obtain a higher density and, therefore, may be preferred for
certain applications.
The methods of increasing the density of bulk materials
result in bulk materials having a density of at least 55 Ibs/ft3
,
with a useful range between about 55 Ibs/ft3 to about 60
lbs/fe.
Methods for improving thermal properties of bulk materials
without reducing density are also provided. The methods
are generally accomplished by first separating the bulk
material into a first size fraction and a smaller size fraction.
30 The smaller size fraction is next separated into a second size
fraction and a third size fraction, in which the second size
fraction is larger than the third size fraction. The second size
fraction is then sized into a fourth size fraction, which is the
same size as the third size fraction. The final step is
combining the first size fraction with the third and fourth
35 size fractions to produce a final bulk material having
improved thermal properties, such as reduced permeability
and increased moisture retention. Optionally, the methods
can also include a step of sizing the starting bulk material
into a desired topsize before separating out a first size
40 fraction.
Preferably, the permeability of the final bulk material is
reduced at least about 50%, more preferably is reduced at
least about 90%, while the moisture retention capacity is
45 increased at least about 25%, more preferably at least about
50%. For coal, the permeability is preferably less than about
0.040 cm/sec, more preferably less than about 0.020 cm/sec,
and most preferably less than about 0.004 cm/sec. In a
further embodiment, the present invention also provides
50 methods for reducing the density of bulk materials. The
density of bulk materials can be reduced by creating more
void space between particles to promote, for example, flow
of gases and liquids between particles. Accordingly, such
methods would be useful for storing or treating bulk mate-
55 rials with chemicals or when exposure to heat, air (i.e.
oxidation), other gases or liquids is desired.
SUMMARY OF THE INVENTION
The present invention relates to methods of controlling
the density, permeability, moisture retention and thermal
properties of bulk materials and to compositions produced
by such methods. Bulk materials that can be controlled by
the present methods include any material that can be fractionated
by particle size and include, for example, solid fuel
materials, limestone, bulk food products, sulfide ores,
carbon-containing materials such as activated carbon and
carbon black. Solid fuel materials include, for example, coal,
lignite, upgraded coal products, oil shale, solid biomass
materials, refuse derived fuels (including municipal and
reclaimed refuse), coke, char, petroleum coke, gilsonite,
distillation byproducts, wood byproducts, shredded tires,
peat and waste pond coal fines.
In one embodiment, the present invention relates to methods
of increasing the density of a bulk material by combining
two different particle sized fractions to form resulting
bulk material having a bimodal size distribution. The methods
are generally accomplished by first separating the bulk
material into a first size fraction and a smaller size fraction.
The smaller size fraction is next separated into a second size
fraction and a third size fraction, in which the second size
fraction is larger than the third size fraction. The second size
fraction is then sized into a fourth size fraction, which is the
same size as the third size fraction. The final step is
combining the first size fraction with the third and fourth
size fractions to produce a densified bulk material.
Optionally, the methods can also include a step of sizing the
starting bulk material into a desired topsize before separating
out a first size fraction.
For example, in one embodiment the method is accomplished
by recovering a first size fraction of the bulk material
having a particle size of about 1 inch to about 2 inches,
followed by recovering a third fraction of the bulk material
having a particle size of less than about Y4 inch from a 60
second size fraction having a particle size of about Y4 inch
to about 1 inch and subsequently crushing, grinding or
pulverizing the second size fraction to form a mixture
having a particle size of less than about Y4 inch. In the final
step, the first, crushed second and third size fractions are 65
combined to produce a higher density bulk material. Mixing
these fractions provides the fine particles an opportunity to
bulk density since the materials are simply crushed into a
smaller size in an attempt to increase the surface area of the
bulk material.
Compacting or vibrating is commonly used to increase
bulk densities by many industrial applications that handle 5
relatively small volumes of high-value fine powders (0.5
mm and smaller). Examples include pharmaceuticals,
cosmetics, ceramics, sintered metals, plastic fillers and
nuclear fuel elements. However, many applications that
involve large volumes of coarse bulk materials (up to 150 10
mm) cannot effectively use compaction or vibration to
control bulk density. If the coarse material is of relatively
high value, expensive oil or other chemical additives that
modify the particle surface characteristics can be applied to
modify bulk density. For example, steel mills typically 15
control bulk density of metallurgical coal feeding cooking
ovens by applying additives as described in U.S. Pat. No.
4,957,596 entitled "Process for Producing Coke."
Accordingly, a need exists for low cost methods of
controlling the density, permeability and moisture retention 20
of bulk materials. The present invention satisfies this need
and provides related advantages.
US 6,786,941 B2
5 6
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, sulfide ores, gravel, rocks and limestone.
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, corn, soybeans,
25 barley, oats and any other grain that are transported and/or
stored.
As used herein, the term "fractionation" refers to the
process of separating different particle sizes of a bulk
material by any means known to those skilled in the art,
30 including, for example, screens with varying mesh sizes or
filters with varying pore size. Such fractionation means can
be made of any suitable material including, for example,
metal, plastics or other polymers with desired apertures (i.e.
pore or hole size). In addition, fractionation using such
35 screens or filters can be facilitated by contemporaneous
shaking or vibrating to speed the fractionation process.
Vibrating screens are particularly useful for dry coarse size
separations 6 mm and greater, the size ranges of interest for
bulk materials such as coal. If finer size separations are
40 desired, cyclones can be used to classify materials between
0.01 and 1 mm. As noted above, the present invention
includes methods of increasing the density of bulk materials
compared to normal densities of naturally-occurring particle
size distributions (for example, 45-50 Ibs/ft3
) as described
45 above. Several benefits result from increasing the density of
bulk materials. For example, increasing the bulk density of
coal from the existing typical value of 50 pounds per cubic
foot by 10% would likely eliminate underweight penalties
described above. Other benefits for rail transport include, for
50 example: (i) lower center of gravity; (ii) smaller and lighter
rail cars; (iii) less total trailing load; (iv) shorter trains; and
(iv) less loading and unloading time. Likewise, barges,
seaway self-unloaders and ocean-going vessels could haul
more tonnage per voyage thus reducing costs. In addition,
55 cold weather operations on the Great Lakes and Upper
Mississippi River, for example, could increase the amount of
coal hauled before ice forces the waterways to close.
One embodiment of these methods involves the use of a
bi-modal size distribution. A bi-modal size particle size
60 distribution is characterized by bulk material having two
discontinuous particle size ranges as depicted, for example,
in FIG. 4. Another way to describe a bi-modal size distribution
is with reference to a graph plotting the total weight
of particles having a first size range against the particle size.
65 Where the particle size distribution is bi-modal, such a graph
will be characterized by two discrete areas under a curve,
each generally having a gaussian shape.
DETAILED DESCRIPTION OF IRE
INVENTION
FIG. 4 is a void-filling depiction of a composition produced
by combining two particle size fractions in which the
composition has a density of 105% of normal and a void
space of 35%.
FIG. 5 is a void-filling depiction of a composition pro- 5
duced by combining two particle size fractions in which the
composition is overfilled with the smaller size fraction
resulting in a density of 95% of normal and a void space of
40%.
FIG. 6 is a void-filling depiction of a composition having 10
mono-sized particles with a bulk density of 85% of normal
and a void space of 45%.
FIG. 7 is a void-filling depiction of a composition produced
by combining two particle size factions in which the 15
composition is underfilled with the smaller size fraction
resulting in a density of 95% of normal and a void space of
40%.
FIG. 8 is a flowsheet of a process for producing high
density bulk materials that includes vibrating screens, 20
double-roll crusher and hammermill.
The present invention provides methods of controlling the
density and thermal properties of bulk materials, and the
bulk materials produced according to the methods. The
density, permeability and moisture retention of bulk materials
can be either increased or reduced by the methods of the
present invention depending on the intended application.
In one embodiment of the present invention, methods of
increasing the density of bulk materials are provided that
result in a reduced overall volume of the build material,
which reduces the amount of space required for transportation
and/or storage. Several factors influence bulk density
including particle shape size distribution, surface
characteristics, the size and shape of the container holding
the bulk material, the manner in which the bulk material is
deposited into the container, and vibration and pressure
compaction.
Particulate bulk materials are a collection of solid particles
and air occupying the interstitial space between the
particles. The percentage of interstitial space or voids
depends on the nesting of the individual particles in relation
to each other. Thus, an ideal particle size distribution provides
sufficient quantity of fine particles to fill the void
spaces surrounding coarse particles. Bulk density (i.e., the
weight of material per unit volume occupied by the material)
is inversely proportional to voids. Accordingly, the various
methods of the present invention are directed to reducing
voids to obtain higher bulk density and increasing voids to
obtain lower bulk density by controlling particle size distribution
in the resulting composition.
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. The term "coal" as used
US 6,786,941 B2
7 8
prepared coarse and fine fractions are combined in proportion
such that the resulting density is 10 percent greater than
the starting or feed bulk material, and preferably greater than
about 55 Ibs/ft3
, with a particularly useful range being
between about 55 Ibs/ft3 to about 60 Ibs/ft3
.
In a further embodiment, the present invention provides
alternative methods of increasing the density of bulk materials.
The methods are generally accomplished by fractionating
the starting bulk material into successively smaller
particle size fractions. The largest of the fractions is first
placed in a container or other holding compartment. The
next smaller size fraction is then added to fill the void
between the larger particles until the smaller particles begin
to dilate the entire mixture and reduces the bulk density. At
that point, the next successive smaller size fraction is added
filling the void until the larger size particles are forced apart
and the mixture begins to dilate. This process is continued
until the smallest size fraction is used. The composition
produced by these methods is depicted in FIG. 3.
An example of this embodiment is shown schematically
in FIG. 2. This process classifies the starting 61 xO" bulk
material into numerous closely sized fractions such as 2xl
inch, lxY2 inch, Y2xY4 inch, Y4xl/s inch and less than l/s inch
fractions. Then, starting with the largest 2xl inch size
fraction, the next smaller lxY2 inch fraction is added filling
the void between the larger particles. Filling is continued
until the smaller particles dilate the mixture. At that point,
the next smaller Y2xY4 inch fraction is added filling the void
until the mixture dilates. This process is continued with the
Y4xl/s inch fraction and finally the minus l/s inch fraction.
The methods of the present invention also provide bulk
materials having improved thermal properties, including
decreased permeability and increased moisture. Decreased
permeability and increased moisture retention favorably
affect the ability of the bulk material to resist forming ice.
Permeability measures the rate at which water flows through
the particulate bulk material. Thus, low permeable materials
tend to hold moisture near the surface exposed to rain and
snow. The higher moisture retention capacity absorbs moisture
before it can saturate the material and form channels.
Accordingly, lower permeability and higher moisture retention
result in greater ice formation near the top of the
conveyance that can be readily discharged from the conveyance
along with the bulk material. In addition, bulk materials
with lower permeability will shed water more effectively
when stored in a storage pile. Thus, more water will run off
the pile rather than being soaked into the bulk material.
Thus, the methods of improving the thermal properties of
bulk materials favorably affect the following two factors that
control the formation of ice in bulk materials: (i) rate of heat
transfer from the warm bulk material to the cold
environment, and (ii) concentration of water (the source
material for ice) on the surface of the bulk material.
With regard to the first factor, ice forms when sufficient
heat transfers from the warm bulk material to the cold
environment. Such conduction heat transfer is evaluated
using Fourier's law as detailed in Reynolds & Perkins,
Engineering Thermodynamics (McGraw-Hill Book Co.,
1970).
In transient heat flow conditions present in transporting
bulk material, the rate of heat transfer by conduction and
60 convection between the bulk material and the environment
is a function of two factors, including the thermal conductivity
and thermal capacitance of the material. Other heat
transfer factors that are independent of the properties of the
bulk material, include surface area exposed to cold
temperatures, temperature difference between the bulk material
and the environment, and time. In a convection heat
transfer system, typical of transporting bulk material in a
Particularly useful particle sizes for these methods meet
the following criteria: (i) limit the largest size (i.e., topsize)
of the coarse fraction to commercial specifications, for
example, for many materials such as coal the topsize is 50
mm; (ii) minimize the quantity of fine fraction to reduce dust 5
and other material handling problems; (iii) maximize the
ratio between coarse and fine fraction particle size to promote
efficient mixing of the two fractions; (iv) match the
void volume in the coarse fraction with the total volume of
the fine fraction; (v) maximize the topsize of the fine fraction 10
to reduce comminations and classification costs; and (vi) use
all the feed material.
Other factors that dictate the selected sizes chosen to
partition the material include (i) breakage characteristics of
the material; (ii) classification efficiency; (iii) material handling
properties of the final product including angle of 15
repose, angle of reclaim, internal angle of friction; (iv)
coherence (i.e., the sticking of particles to one another); (v)
rate of production; and (vi) final product bulk density
specifications.
As an example, the methods of this embodiment can be 20
accomplished by the process schematically depicted in FIG.
1. As shown in FIG. 1, the raw bulk material ranging from
6 inches and less (6 I xO") is first fractionated with a screen
having a 2 inch aperture to separate less than 2 inch fractions
(-2I xO") from fractions having 2 inches and more (6 I x2"). 25
This latter fraction is further crushed, ground or pulverized
to produce fractions having -2I xO" fractions and combined
with the classified -2I xO" fraction. The term "classified"
refers to the fraction that falls through the apertures of the
fractionation device (such as a screen) as opposed to a 30
fraction that is crushed, ground or pulverized to that size.
Such fractions can be crushed, ground or pulverized according
to any method known to those skilled in the art
including, for example, using a roller crusher with variable
speed drive and gap settings.
35 The resulting -2I xO" fraction is then fractionated with a
screen having a 1 inch aperture to separate less than 1 inch
fractions (-l l xO") from the -2I xl" fraction. The -2I xl"
fraction is also referred to herein as the "coarse fraction."
The -l l xO" fraction is further fractionated with a screen
having a Y4 inch aperture to separate fractions of less than Y4 40
inch (-Y4l xO") from the -l l xY4" fraction, also referred to
herein as the third or intermediate fraction. This intermediate
fraction is then crushed, ground or pulverized to produce
fractions of -Y4l xO", which is then combined with the
classified -Y4l xO" fractions to produce the "fine fraction." 45
The coarse fraction is then blended with the fine fraction to
produce the desired bi-modal bulk material having a first
size ranging from about 1 inch to about 2 inches, and a
second particle size range of less than Y4 inch. These
conditions have been found by experiment to produce the 50
highest bulk density while satisfying the criteria listed
above.
A surprising discovery was made when testing the densities
of (i) the classified -Y4l xO" fraction, (ii) the crushed
third fraction to produce a -Y4 l xO" fraction, and (iii) the 55
combined fine -Y4 l xO" fraction. The density of the classified
fraction (i) was determined to be about 44 lbs/fe and the
density of the crushed fraction (ii) was determined to be
about 41 lbs/fe. However, the combined fraction (iii) was
surprisingly determined to be 50 lbs/fe.
The proportion of coarse fraction is selected so that the
void volume is slightly less than the volume of the fine
fraction. In addition, the particle size difference between the
coarse and fine fractions is maximized to promote efficient
flow of the fine particles into the coarse fraction void. In a 65
preferred embodiment, approximately 86% of the coarse
fraction void is filled with the fine fraction. Preferably, the
US 6,786,941 B2
9 10
EXAMPLE 1
Subbitiminous Coal
The bulk density of a sized coarse material increases by
adding sufficient fine particles to fill the void surrounding the
coarse particles. Successively finer particles can be used to
fill the resulting voids until the entire mass dilates. The
midsize fraction, l-xY2-inch size fraction, was not added.
Table 1 lists bulk density measurements obtained for
Powder River Basin subbituminous coal by adding increasing
amounts of various fine (minus Y2-inch) size fractions to
2-xl-inch size fraction.
tionship between void space and permeability for a desired
density can be readily determined by those skilled in the art.
For many bulk materials, such as sulfide ores and
limestones, for example, the void space can be increased
5 from 30% to 50% by reducing the concentration of fine
particles.
Void space can be increased by removing fine particles or
increasing the proportion of coarse particles in the bulk
material. For example, screening out or agglomerating fine
10 particles will increase the void. As an alternative, one or
more selected or predetermined size fractions can be added
to the bulk material in sufficient quantity to "overfill" the
void to dilate the entire material. In addition, certain
crushers, such as roll crushers and jaw crushers, can be used
15 to create fewer fine particles than crushers and pulverizers
that use impact as the primary crushing force. These various
methods can be used to obtain bulk materials having densities
that are less than normal densities as depicted, for
example, in FIGS. 5, 6 and 7.
The present methods for reducing the density of bulk
materials would be useful for storing or treating bulk materials
with chemicals or when exposure to heat, air (i.e.
oxidation), other gases or liquids is desired. These methods
25 are particularly desirable when advantageous chemical reactions
take place between solids and the gas or liquid.
Applications for such methods include, for example, leaching
ores with acid and cyanide solutions, or roasting materials
with hot gases in fluid-bed reactors.
The following examples are intended to illustrate, but not
limit, the present invention. In the following examples,
samples of bituminous coal, subbituminous coal, lignite and
limestone were tested to increase bulk density by modifying
particle size distribution. In many cases, the bulk density
35 was increased by 10 percent by modifying the particle size
distribution. The bulk density of existing commercial coal
and lignite ranges from 45 to 50 pounds per cubic foot
(PCF). The bulk density of crushed limestone ranges from
105 to 110 PCP.
conveyance, heat transfer between the bulk material and the
environment occurs when cold air passes over the exposed
surface of the warm bulk material and cools the surfaces of
the conveyance that are in contact with the bulk material.
By decreasing the permeability and increasing the density
of a bulk material according to the methods of the present
invention, heat transfer by cold air passing over the exposed
surface of the bulk material is significantly reduced.
Decreasing permeability impedes the flow of cold air from
the cold environment into the interstitial space between
particles of the bulk material. Impeding flow reduces the
mass of air available to transfer heat and reduces the average
velocity of air moving through the interstitial spaces.
According to fundamentals in heat transfer, the quantity
of heat transferred from a warm solid to a moving fluid, such
as air, decreases as mass and velocity of the fluid decreases.
Increasing bulk density provides more mass per unit volume.
This effect proportionally increases thermal capacity,
which is the ability of a material to resist changing temperature.
In other words, for a given heat transfer condition, 20
a massive material with a higher thermal capacity will
experience a lower temperature change than a less massive
material with a lower thermal capacity. Therefore, reducing
the rate of heat transfer by convection and providing greater
thermal capacity creates a condition less favorable to forming
ice.
As noted above, the second factor that affects the formation
of ice is water concentration. Water concentrated on the
surface of bulk materials (surface moisture) is the source for 30
ice. Surface moisture has two principal sources: (i) water
introduced during processing (typically between two and
five weight percent concentration), and (ii) rain and snow
falling during transport.
Ice usually forms where liquid water has pooled. Surface
moisture introduced during processing is distributed
throughout the bulk material, so pooling is not usually a
problem from this source. Water introduced by rain and
snow flows from the exposed surface throughout the bulk
material and congregates in pools. Pooled moisture near 40
cold exposed surfaces of the conveyance can freeze to form
ice, particularly at the bottom of the conveyance. The frozen
pools makes discharging the bulk material from the conveyance
difficult. In contrast, the methods of the present invention
result in greater ice formation near the top of the 45
conveyance that can be readily discharged from the conveyance
along with the bulk material.
The present invention further provides methods of reducing
the density of bulk materials. The density of bulk
materials can be reduced by creating more void space 50
between particles to promote, for example, the flow of gases
and liquids between particles. Thus, the permeability of the
bulk material increases as void space increases. The rela-
TABLE 1
Bulk Density Results for Various
Combinations of Size Fractions
Powder River Basin Subbituminous Coal
Cumulative Weights (kg)
Yzinch
x Loose Bulk
Size Fraction Weight Added, 2-inch x 1- V4- Density
Step Added kg inch inch [I.-inch x 6M 6M x 14M 14M x 0 (peF)
1 2x1 13.00 13.00 0.00 0.00 0.00 0.00 40.7
2 Y2 x Y4 3.00 13.00 3.00 0.00 0.00 0.00 44.3
US 6,786,941 B2
11
TABLE 1-continued
Bulk Density Results for Various
Combinations of Size Fractions
Powder River Basin Subbituminous Coal
Cumulative Weights (kg)
12
Size Fraction Weight Added, 2-inch x 1-
Step Added kg inch
V2inch
x
Y4inch
V4-inch x 6M 6M x 14M 14M x 0
Loose Bulk
Density
(PCF)
3 112 X Y4 3.00 13.00 6.00 0.00
6 1/4 x 6M 6.00 13.00 6.00 6.00
7 1/4 x 6M 3.00 13.00 6.00 9.00
8 6 x 14M 6.00 13.00 6.00 9.00
9 6 x 14M 6.00 13.00 6.00 9.00
10 6 x 14M 5.29 13.00 6.00 9.00
12 14M x 0 12.00 13.00 6.00 9.00
13 14M x 0 12.00 13.00 6.00 9.00
Results demonstrate that bulk density increases as fines
are added to fill the void around course particles. Step 13
product was chosen for additional investigation because it 30
had the highest bulk density, 56.3 PCF, of any product
produced by the experiment.
Table 2 compares the particle size distribution and bulk
density of typical commercially available 2-inchxO Powder
River Basin subbituminous coal to the sample prepared in 35
Step 13 of Table 1.
TABLE 2
0.00 0.00 49.2
0.00 0.00 48.8
0.00 0.00 49.1
6.00 0.00 49.6
12.00 0.00 49.7
17.29 0.00 49.8
17.29 12.00 54.8
17.29 24.00 56.3
A sample of 6-inchxO Powder River Basin subbituminous
coal was screened and crushed similarly to coal processed
by the flowsheet shown in FIG. 8. The flow rates indicated
next to each flowstream were computed based on crushing
tests and screen manufacturer's performance data. Table 3
lists the estimated particle size distribution of final highdensity
product produced by the flowsheet. A 20-kg sample
representing the final high-density product was prepared by
combining various size fractions together in the proportions
listed in Table 3.
Comparison of Commercial 2-inch x 0
and
Specially Prepared High-Density Powder
River Basin Subbituminous Coal
Direct Weight Percent
40
TABLE 3
Size Distribution of High Bulk Density
Powder River Basin Subbituminous Coal Product
Produced by Screening and Crushing
Size Fraction
Plus 2-inch
2 x 1 inch
1 x V2 inch
Y2 x Y4 inch
V4 inch x 6M
6M x 14M
14M x 0
Bulk Density
(loose)
Commercial
Coal
4%
21%
23%
20%
12%
11%
10%
49.5 PCF
EXAMPLE 2
Step 13 Table
1 High Density
Formulation
0%
19%
0%
9%
13%
25%
35%
56.3 PCF
45
50
55
Size Fraction
Plus 2-inch
2 x 1 inch
1 x 112 inch
Y2 x Y4 inch
V4 inch x 6M
6M x 14M
14M x 0
Bulk Density
(loose)
EXAMPLE 3
High Bulk
Density
Product
1%
36%
2%
10%
20%
18%
13%
56.4 PCF
Subbituminous Coal
A commercial process using a combination of vibrating 60
screens and crushers could be developed to produce a
high-density product similar to the sample listed in Step 13
in Table 1. FIG. 8 shows a possible process flowsheet that
includes vibrating screens, double-roll crusher and hammermill.
The process shown in FIG. 8 mixes a coarse fraction 65
(2-x1-inch) with a fines fraction (Y4-inchxO screenings with
crushed material) to form the high-density product.
Bituminous Coal
A sample of%-inchxO Utah bituminous coal was tested to
measure how changes in particle size distribution affected
loose bulk density. Table 4 compares the size distribution of
commercial minus %-inch product with a sample of a
specified particle size distribution designed to produce a
high bulk density.
US 6,786,941 B2
13
TABLE 4
14
TABLE 5
Comparison of Commercial 3/4-inch x 0 and
Specially Prepared High Density Utah Bituminous Coal
Direct Weight Percent
5
Size Distribution of High Bulk Density
Texas Lignite Product
Produced by Screening and Crushing
Size Fraction
Plus 314-inch
3/4 x Y4 inch
Y4-inch x 8M
8M x 28M
28M x 0
Bulk Density
(loose)
Natural
Crushed Coal
3%
30%
27%
24%
16%
54 PCF
EXAMPLE 4
Lignite
High Density
Formulation
14%
39%
21%
15%
10%
59.7 PCF
10
15
20
Size Fraction
Plus liz-inch
Y2 x Y4 inch
Y4 inch x 8M
8M x 10M
10M x 28M
28M x 0
Bulk Density
(loose)
EXAMPLE 6
High Bulk
Density
Product
18%
15%
19%
6%
15%
27%
55.0 PCF
A sample of%-inchxO Texas lignite was tested to measure
how changes in particle size distribution affected loose bulk 25
density. Table 5 presents a particular size distribution that
produced the relatively high bulk density of 55.0 PCP. The
bulk density of typical lignite produced by a commercial
mine ranges from 45 to 50 PCP.
Limestone
Table 6 lists bulk density measurements obtained for
crushed limestone by adding increasing amounts of various
fine (minus %-inch) size fractions to a l-x%-inch size
fraction.
TABLE 6
Bulk Density Results for Various Combinations
of Size Fractions Crushed Limestone
Cumulative Weights (kg)
Size Fraction Weight Added,
l-inch x inch x Loose Bulk
Density
Step Added kg inch inch 1!4-inch x 8M 8M x 28M 28M x 0 (PCF)
1 x '14 12.52 12.52 0 0.00 0.00 0.00 90.5
2 3/4 X Y4 2.18 12.52 2.18 0.00 0.00 0.00 91.0
3 3/4 X Y4 2.18 12.52 4.36 0.00 0.00 0.00 91.5
3/4 x Y4 3.5 12.52 7.86 0.00 0.00 0.00 91.2
7 Y4 x 8M 5.47 12.52 7.86 5.47 0.00 0.00 96.9
8 Y4 x 8M 5.53 12.52 7.86 11.00 0.00 0.00 104.5
9 Y4 x 8M 5.35 12.52 7.86 16.35 0.00 0.00 105.7
10 Y4 x 8M 11.00 12.52 7.86 27.35 0.00 0.00 106.1
12 8M x 28M 15.34 12.52 7.86 27.35 15.34 0.00 110.2
13 8M x 28M 15.30 12.52 7.86 27.35 30.63 0.00 110.8
14 8M x 28M 15.26 12.52 7.86 27.35 45.89 0.00 110.3
15 28M x 0 22.79 12.52 7.86 27.35 45.89 22.79 112.7
16 28M x 0 7.60 12.52 7.86 27.35 45.89 30.38 117.8
17 28M x 0 7.60 12.52 7.86 27.35 45.89 37.98 119.2
18 28M x 0 14.96 12.52 7.86 27.35 45.89 52.94 118.4
19 28M x 0 7.60 12.52 7.86 27.35 45.89 60.54 118.0
US 6,786,941 B2
15
EXAMPLE 6
16
B. Thermal Capacity Tests
Approximately 185-kg of commercial sub-sample was
loaded into a 7.70 cubic-foot capacity (55-gallon) poly
drum. Approximately 206 kg of high-density sub-sample
was loaded into a similar drum. Each drum, measuring
24-inches in diameter and 36-inches high, was filled within
2 inches of the top rim.
Two platinum resistance temperature detector (RTD)
probes were inserted into each sample to measure material
temperatures. The first probe was inserted along the vertical
centerline 24 inches into the material to measure temperatures
at the center of mass. The second probe was inserted
Commercial Sample High-Density Sample
Properties of Typical Commercial and
High-Density Subbituminous Coal Samples
Study of Middle-Sized Particles
An experiment was conducted using subbituminous coal 5
to measure the effect of changing the concentration of
middle sized particles on bulk density. Naturally broken
material contains middle size particles, which may account
for natural materials consistently having a lower bulk density
than the higher bulk density compositions consisting of 10
coarse and fine particles described herein. An equal ratio of
fine and coarse particles was chosen as a mixture that
produces a high-density product. The middle size particles
dilute the fixed amount of fine and coarse particles. The
coarse size fraction was 2-xl-inch, the middle size fraction 15
was l-xY4-inch, and the fine particle fraction was minus
Y4-inch screenings. Coal with minimal surface moisture was
used. The bulk density container was lightly tapped as it was
filled.
The results of the experiments, as listed in Table 7, are 20
consistent with the concept that middle size particles affect
bulk density by impeding flow of fines particles into voids.
Middle size particles further reduce bulk density by forcing
large particles apart.
Parameter
Plus 314-inch wt %
3/4- x V4-inch wt %
Minus Y4-inch wt %
TABLE 8-continued
32% 32%
28% 0%
40% 68%
TABLE 7
Changes in Bulk Density Resulting from
Varying Concentration of Middle Size Fraction Concentration
2-inch x 0 PRB Subbituminous Coal
Bulk Density
Results (lightly tappedl
Volume Bulk Density
(cu ft) (lb/cu ft)
Weights (kg) Weight Percents
Coarse Middle Fine - 1;4 inch Coarse Middle Fine - Y4 inch
2 xl" 1 x W' screenings 2 x 1" 1 x W' screenings
14.37 0.00 0.00 100% 0% 0%
0.00 15.82 0.00 0% 100% 0%
0.00 0.00 15.92 0% 0% 100%
10.00 0.00 10.00 50% 0% 50%
10.00 2.00 10.00 45% 9% 45%
10.00 4.50 10.00 41% 18% 41%
10.00 12.00 10.00 31% 38% 31%
3.60 10.80 3.60 20% 60% 20%
Total Wt
(kg)
14.37
15.82
15.92
19.39
18.98
18.84
18.25
17.07
0.73
0.73
0.73
0.73
0.73
0.73
0.73
0.73
43.4
47.8
48.1
58.6
57.3
56.9
55.1
51.6
TABLE 8
EXAMPLE 7
Thermal Capacity
A. Sample Description
A 400-kg bulk sample of nominal minus 2-inch subbituminous
coal obtained from an operating coal mine was split
into two 200-kg sub-samples. The first sub-sample represented
a typical commercial bulk material commonly
shipped from mines in rail cars. The second sub-sample was
processed to obtain a high-density, low-porosity material at
least 10 percent greater than commercial products. Table 8
lists material properties of the typical commercial and
processed subbituminous coal.
Bulk density
Porosity, Volume %
45 at a point 6 inches from the wall of the drum and 12 inches
into the material to measure temperatures along the outer
wall of the drum. The RDT probes were connected to an
automatic data acquisition system to monitor and log temperatures
for the duration of the experiment.
50
The commercial and high-density sample drums were
placed into a sealed insulated enclosure. The interior temperature
of the enclosure was maintained between 10 and
15° F. cooler than the initial sample temperature. Sample
55 temperatures were recorded until the sample cooled to
approximately the same temperature as the enclosure.
The rate of temperature change, an important parameter
that characterizes a sample's thermal properties in transient
conditions, was determined from noting changes in succes-
60 sive temperature readings taken at 6 inches from the wall of
the container. Table 9 lists the rate of temperature change for
the initial 16 hours for commercial and high-density
samples. When exposed to cold temperatures, warm commercial
sample in proximity of the wall cools more readily
65 than the warm high-density sample. This fact demonstrates
that the commercial bulk material will freeze more quickly
than the high-density bulk material.
53 PCF 59 PCF
32 volume % 24 volume %
Properties of Typical Commercial and
High-Density Subbituminous Coal Samples
Parameter Commercial Sample High-Density Sample
US 6,786,941 B2
17
TABLE 9
Rate of Temperature Change CF./hr)
at 6 Inches from Wan 30e F. Ambient,
60° F. Initial Sample Temperature
18
repeated with treated high-density coalof 61 pounds/cubic
foot. Samples of dry untreated and treated high-density coal
were immersed in water and drained on a fine-mesh screen.
The amount of moisture retained in the samples was mea-
5 sured. Results of the permeability and moisture retention
tests are summarized in Table 11.
Time,
Hours
Commercial
Sample
High-density
Sample Difference, 0 F./hr TABLE 11
Permeability and Moisture Retention
of Untreated and Treated Bituminous Coal Sample
Start (0 hrs)
1 hours
3 hours
4 hours
8 hours
0.00
-0.10
-0.68
-0.79 (peak rate)
-0.50
0.00
-0.05
-0.12
-0.28
-DAD (peak rate)
0.00
0.05
0.56
0.51
0.10
10
Test
Untreated,
55 PCF
Treated
61 PCF % Change
Decreased
92%
Increased
54%
* *
21.1% moisture
* * *
42 x 10-3 em/sec 3.2 x 10-3 em/sec
13.7% moisture
40
While various embodiments of the present invention have
been described in detail, it is apparent that modifications and
adaptations of those embodiments will occur to those skilled
in the art. It is to be expressly understood, however, that such
modifications and adaptations are within the scope of the
present invention.
What is claimed is:
1. A method of increasing the density of a bulk material,
comprising the steps of:
(a) separating the bulk material into increasingly smaller
sized fractions of the bulk material;
(b) placing the largest sized fraction into a confined area;
(c) adding a second sized fraction to the largest sized
fraction until the second sized fraction begins to dilate
the largest sized fraction to form a first combined
material; and
(d) adding successively smaller sized particle fractions to
the first combined material until each addition begins to
dilate a previous combined material to produce a final
bulk material having a desired density.
2. The method of claim 1, wherein said material is a bulk
fuel material.
3. The method of claim 2, wherein said bulk fuel material
45 is coal.
4. The method of claim 3, wherein the coal is bituminous
coal, subbitummous coal, or lignite.
35
30
Permeability,
15 em/sec
Moisture
content at
saturation, wt %
moisture
61 PCF
23 volume %
40%
0%
High-Density
Sample
Commercial
Sample
55 PCF
31 volume %
30%
40%
TABLE 10
Properties of Typical Commercial and
High-Density Bituminous Coal Samples
Parameter
Bulk density
Porosity, Volume %
Plus Yz-ineh wt %
V2-inch x 6-
mesh wt %
B. Permeability and Moisture Retention Tests
Samples of dry commercial and high-density bituminous
coal were loaded into a round pipe 15.2 cm in diameter to
a depth of 36 cm. The round pipe was fitted with a fine mesh
screen on the bottom, and was open on the top.
The pipe was filled with untreated coal, and 1,500 ml of
water was quickly poured on top of the sample, forming a
pool approximately 8 cm deep. The time required for the
water to flow into the sample was noted. The experiment was
EXAMPLE 8
A. Sample Description-Permeability and Moisture Retention
Experiments
A 20-kg bulk sample of nominal minus %-inch bituminous
coal obtained from an operating fossil-fired power 20
plant was split into two lO-kg sub-samples. The first subsample
represented a typical bulk material commonly used
as fuel at fossil-fired power plants. The second sub-sample
was processed to obtain a high density, low porosity material
at least 10 percent greater than commercial products. Table 25
10 lists material properties of the typical commercial and
processed bituminous coal.