6,786,941 Methods of controlling the density and thermal properties of bulk materials

Patent Number/Link:

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

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 *

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

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

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.

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%.

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

TABLE 1-continued

Bulk Density Results for Various

Combinations of Size Fractions

Powder River Basin Subbituminous Coal

Cumulative Weights (kg)

Size Fraction Weight Added, 2-inch x 1-

Step Added kg inch

V2inch

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

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

21%

23%

20%

12%

11%

10%

49.5 PCF

EXAMPLE 2

Step 13 Table

1 High Density

Formulation

19%

13%

25%

35%

56.3 PCF

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

36%

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

TABLE 4

TABLE 5

Comparison of Commercial 3/4-inch x 0 and

Specially Prepared High Density Utah Bituminous Coal

Direct Weight Percent

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

30%

27%

24%

16%

54 PCF

EXAMPLE 4

Lignite

High Density

Formulation

14%

39%

21%

15%

10%

59.7 PCF

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%

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

EXAMPLE 6

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

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.

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

TABLE 9

Rate of Temperature Change CF./hr)

at 6 Inches from Wan 30e F. Ambient,

60° F. Initial Sample Temperature

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

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

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;

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.

Permeability,

15 em/sec

Moisture

content at

saturation, wt %

moisture

61 PCF

23 volume %

40%

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.