Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED COMPOSITION AND PROCESS
FOR AGGLOMERATING COAL PARTICLES
Field of the Invention
The present invention relates to an improved
composition and process for agglomerating coal particles. More
particularly, the present invention relates to a process of
selectively adding fiber and hydrophobic binder to coal
particles to increase the strength and Moisture repellency of
agglomerates formed from the coal particles.
Background of the Invention
In the mining and processing of coal, small particles
of coal known as "coal fines" are randomly produced as the coal
is handled. Coal fines are usually defined as coal particles
having a diameter less than 590 microns. In addition to
randomly produced coal fines, coal is often beneficiated to a
small particle size`to permit the separation of minerals and
inorganic sulphur from the coal.
Coal fines are difficult to handle and to transport
because of lack of cohesion among the coal particles. Because
coal is ireq~ently transported by open conveyors or by rail
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cars, coal fines are difficult to transport without loss of coal
due to "dusting efEects." The coal loss increases as the
partlcle size of the coal decreases. To lessen the amount of
coal lost during transportation, the particle size of the coal
may be increased by various manufacturlng processes such as
briquetting, extruding, or by pressurizlng the coal into pellets
or pucks. Preferably, the agglomerated coal particles formed by
such processes should be sufficiently strong to resist breaking
into fine coal as the particles are handled. In addition, the
agglomerated coal particles should resist moisture sorption9 due
to rain or high humidity, which would decrease the
combust~bility of the coal.
Various techniques have been developed for increasing
the size and strength of coal particles. In U. S. Patent
Number 181,003 to Reinold (1913), a large quantity of moisture
and dry paper pulp was added to fine coal before the coal was
pressed into brlquets. In U. S. Patent Number 2,066,457 to
Decker (1935), water was added to waste paper to form a pulp.
Subsequently, 67 parts of pulverized coal were added to 21 parts
of the pulp, excess water was removed from the mixture, and 12
parts of asphalt wëre added as a binder before the mixture was
compressed into a briquet. Because these processes add a large
amount of papër and other organic matter to the coal, the amount
of moisture absorbed by the coal significantly increases. The
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additional moisture reduces the combustlbility of the coal and
increases the amount of residual ash created during the
combustion of the coal.
Other techniques have been developed to agglomerate
coal particles without increasing the moisture sorption of the
particles into an agglomerated particle. For e~ample, asphalt
pitch, residual oil; coal tar, and starch have been used to bind
coal particles. In U. S. Patent Number 4,126,426 to Verschuur
(1978), a slurry of coal particles was divided~into a first
fraction of small particles and a second fractlon of large
particles. 10 parts of a liquid hydrocarbon binder was added to
90 parts of the first fraction, and the first fraction was
recombined with the second fraction. The resulting agglomerate
formed by this process reduces the amo~mt of moisture absorbed
by the coal after the excess water has been removed. However,
the resulting agglomerate is susceptible to breakage and to
abrasive wear which degrades the shape of the agglomerate during
transportation of the coal.
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Currently available processes for agglomerating coal ¦
particles are not commercially practical due to several
factors. Processes which use large amounts of organic fiber to
agglomerate coal particles are subject to moisture sorption, and
processes which combine a hydrocarbon binder with coal particles
are subject to breakage. Other processes which combine large
quantities of organic fiber with large quanti-i&s of a
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hydro~arbon binder are expensive to use and may not adequately
reduce moisture sorption to desirable levels. Therefore, a need
exists for an improved composition and process which
agglomerates fine coal particles while ma~imi2ing the strength
and moisture repellency of the agglomerated particles.
SUMMARY OF THE IN~ENTION
The present invention furnishes an improved composition
lU and process for agglomerating fine coal particles which improves
the strength of the agglomerated particles while preventing the
sorption of an undesirable amount of moisture. The composition
comprises between one and five percent fiber by weight of coal
combined with between three and twelve percent hydrophobic
binder by weight of coal. In a preferred embodiment of the
invention, the fiber is organic.
The improved process is practiced by dispersing on the coal
a hydrophic binder of between three and twelve percent by weight
- 20 o~ coal. Subsequently, between one and five percent of fiber by
weight of coal is mixed with the coal and binder, and the coal,
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binder, and fiber are formed into an agglomerate. In an
alternative embodiment of the invention, moisture is removed ~
from the coal particles until the moisture con;tent i5 less than
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tweLve percent. In another embodiment of the invention, the
coal, binder, and fiber are nli~ed with additional coal particles
having a diameter greater than 590 microns before the
agglomerate is formed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As set forth above, known processes do not permit the
economic manufacture of a coal agglomerate which has acceptable
mechanical strength and moisture repellency. The present
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invention accomplishes these objectives by adding between three
and twelve percent by weight of a hydrophobic binder and between
one and five percent by weight of organic fiber to the coal.
To practice the invention, the moisture content of fine
coal is modified to a selected amount which is preferably
between t~o and twelve percent by wei~ht. Moisture can be added
by spraying water onto the coal or can be removed by f~Ltration
or thermal drying techniques well-known in the art.
29 Subsequently, a hydrophobic binder such as fatty acid residues,
sulphite lignin, asphalt, pitch, tar or other hydrocarbon is
added to the coal. Preferably, the hydrophobic binder is
between two and twelve percent by weight of the coal In one
embodiment of the invention, the binder can be:added to the coal
before the moisture is removed from or added to the coal. The
binder should be adequately mixed with the coal to obtain
uniform distribution of the binder. The mixing can be
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accomplished by techniques well-known in the art which include
auger mixing or ribbon blending. If the binder is a petroleum
distillation residue such as pitch~ the binder can be heated and
sprayed onto the coal with an atomizing nozzle.
Following the addition of the binder to the coal, a
fiber having a weight between one and five percent of the coal
is mixed with the coal and binder. The fiber can be one of many
materials and may be organic or inorganic in nature. Examples
of organic fiber include shredded paper, pulverized bark, or
wood was~e produced from a sawmill or lumber dressing plant.
Scrap newsprint is useful because it contains a lov amount of
mineral flller. In addition, scrap cra~t or sulphite paper may
also be used if the combustion of such paper does not result in
an unacceptable amount of ash. The waste fiber can be milled by
a blade mill or by beaters to separate individual fibers and
fiber bundles. During the milling process, the comminuted
fibers may be separated by well-known pneumatic classification
techniques. Waste fiber having an excessively high mois-ture
20 content may ~e partially dried before the fiber is milled. ~ ;
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Following the addition of the fiber to the coal and
binder, the mixture is formed into an agglomerate by techniques
well-known in the art. For example, the mixture may be Eormed
or compressed into briquets, pellets, or may be extruded into
other shapes. Preferablys the agglomerate forming pressure
should exceed 8000 psi. In a puck-forming process disclosed in
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U. S. Patent Number 4,420,404 to Dravo, a flotation concentrate
slurry is thickened and then is loaded into an enclosed
compression chamber. A compressive force expresses fluid from
the chamber until a coarse puck is formed.
The following three examples are presented to
illustrate tests which demonstrate the advantages of the current
invention.
Exc~mple 1
In this test, fine coal flotation concentrate (85%
passing a 200 mesh screen) was filtered,.air dried to 4%
moisture, and mechanically mixed with a commercial asphalt
emulsion (65% asphalt, 35% water) irl an amount equal to 670
asphalt by weight. To this mixture was added 5% by weight
of commercial shredded newsprint, and the whole mixture was
dispersed with an auger mixer. Portions of the mixture were
then formed at 10,000 psi pressure in a 1/2" diameter
cylindrical die. Similar mixtures were prepared without
fiber and according to the methods disclosed by the U~ S.
Patents issued to Decker and Reinold tsee above). The
results of the tests may be summarized as follows:
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TABLE 1
COMPOSITION PRODUCT MOISTURE COMPRESSIVE
_ SORPTION, WT.%STRENGTH (lb)
1. 6% asphalt, 5% fiber 2.1 174
2. 6% asphalt 14.6 68
3. Method of Decker 41.7 462
4. Method of Reinold 28.9 207
(5% fiber)
As demonstrated by these results, Composition I shows
an improvement oE L50% over Composition 2 in strength due to
the added fiber and also shows a large reduction in moisture
sorption (14.6% sorption for asphalt binder ODly, VS. 2.1
sorption for the ~lethod of the present invention). ~he
extremely low water sorption in this test is considered due
to action of the dry fiber in "blotting" residual moisture
from coal surfaces, thereby allowing very effective wetting
of the naturally hydrophobic coal surface by the asphalt
binder. :
Composition 3 showed very high initial strength (462 lb
load to failure vs. 174 lb for Composition 1~, but water
sorption is considered to be unacceptably high at 41%.
Composition 3 also contains large amounts of additive
materials (20% fiber, 12% asphalt) which are expensive when
compared to the market value of the final coal product.
Composition 4 showed a compressive strength which was
18% greater than that of Composition 1. ~owever, the water
sorption of Composition 4 was significantly greater than for
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Composition 1. Therefore, Composition 1 demonstrated the
most favorable combination of co~pressive strength and
resistance to moisture sorption.
Example 2
Agglomerates were prepared from a coal slurry pursuant
10 to the method disclosed by Dravo (see above). Samples were
prepared with no additive, with asphaltic pitch binder as an
additive, and with three different amounts of fiber combined
with pitch binder. Test results were as follows:
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TABLE 2
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SAMPI.E ~ FORMING AS FORMED MOISTURE DROP FILTRATE
PARTICLE SIZE ADDITIVES -PRESSURE MOISTURE RESORPTION TEST LOSS
(kpsi) (%) (%) (%<1/4") (%:-of :
~ coal)
(Scavenger
Concentrate
100 mesh x 0,
20 60% - 325 mesh~ 1. none 16 14.2 9.4 10.1 20.1
2. Pitch, S~ 16 10.1 6.1 7.8 22.0
3. P,itch, 5% 14 11.3 6.8 8.1 ~21.4
4. Pitch, 5% 14 13.3 6.~ 7.4 1.2
Fiber, 1%
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5. Pitch, 5% 14 13.3 7.3 4.2 2.1
Fiber, 2%
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6. ~itch, S% 14 14.6 7.8 1.4 2.7
Fiber~ 3
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With respect to agglomerate strength, a modified ASTM
drop/shatter test was used in this case (increasing strength
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is indicated by decreasing amounts of 1/4" material). As
demonstrated by Compositions 4 - 6, increasing levels of
fiber additive in the 1-3% range progressively improved the
strength of the agglomerate as compared to the strength of
agglomerate formed without binder or with pitch as a
binder.
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In Composition 29 the reduced moisture sorption due to
fiber is not observed as in Example 1. Rather, the tests
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indicate an increase in moisture sorption associated with
increasing levels of fiber additive. ~owever, the amount of
filtrate loss during formation oE the agglomerate was
significantly reduced with the addition of between one and
three percent of fiber to the composition. ~Therefore, the
tests demonstrate that the addition of fiber and binder in
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Compositions 4 - 6 improved the strength of the agglomerate,
reabsorbed less moisture than an agglomerate formed without
any additives, and signlficantly lessened the percentage of ~ ;
coal lost due to filtration during agglomerate formation.
Example 3
Coarse (1/4" x Z8 mesh) coal was blended with the
flotation product slurry used in Example 2 to model a
consolidated product consisting of coarse and fine coal.
The consolidated coal was then agglomerated by the same
method used in Example 2. Test results were as follows:
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TABLE 3
S~MPLE & FORMING AS FORMED MOISTURE DROP FILTRATE
PARTICLE SIZE ADDITIVES PRESSURE MOISTURE RESORPTION TEST LOSS
(~psi) (~) (%) (%<1~4") (% of
coal)
Blended Gravity Pitch, 5% 14 8.1 5.2 6.0 3.9
& Flotation Fiber, 1%
Product Fiber t
1% 1/4" x 0,
2870 - 325 Mesh
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Compared with test 4 of Example 2, the amount of
mo;sture resorbed was reduced from 6.9 to 5.2%. The
strength ;mproved from 7.4 to 6.0 (%<1/4"), although
filtrate loss increased from 1.2% to 3.9%. This data
demonstrates that satisfactory agglomerates can be formed
from a combination of coarse coal, such as coal having a
particle si~e greater than 590 microns, together with a
mixture of fine coal, binder, and fiber.
The present invention discloses a unique composition
and process for agglomerating coal partlcles such as coal
fines. The composition is sufficiently strong to resist
breakage while resisting unacceptable molsture sorption which
would require drying of the coal. The composltion can be ~ ~
25 compressed or otherwise formed into agglomerates by techniques ¦
well-known in the art. Because the cost of fiber and~
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hydrophobic binder often e~ceeds the cost of coal~ the invention
improves the economics of agglomerating coal particles by
significantly reducing the amount of fiber and binder added to
tne coal.
It should be apparent from the foregoing that many
other variations of the composition and process described herein
may be made without departing from the scope of the present
invention. Accordingly, it should be understood that the -~
10 embodiments set forth herein are illustrative and should not :
limit the scope of the invention.
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