Note: Descriptions are shown in the official language in which they were submitted.
~2~
PROCESS FOR BURNIN& A CA:EIBONACEOUS SLURRY
The present invention relates to the burning of
carbonaceous slurry, particularly coal slurries.
Coal is a major source of energy in the United States. It
is increasing in importance b~cause of its abundance within the
United States and because of the security and balanc~ of
payment problems which arise from reliance upon foreign oil.
Transport problems constitute one of the major
difficulties in the use of coal. Many attempts have been made
to solve this problem by preparing slurries of coal with
carrier liquid and pumping said slurries from one point to
another. The slurries so prepared, however, are often
unpumpable at solids contents exceeding about 50 weight
percent.
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The prior art appears to disclose that, in coal-water
slurries, when the solids content exceeds a certain critical
value, the slurry becomes very viscous and unpumpable.
An early patent, issued in September of 1920, places
this critical value at about 20 weight percent of coal. U.~.
patent 1,390,230 of Bates discloses that "Attempts have been
made to carry or force coal through pipes by means of water,
but owing to rapid sedimentation it has been possible to convey
as a maximum only about 20% by weight of particles under
considerable head of water travelling some twenty feet per
second. Save under such exceptional circumstances or in
rivers, water has not served as a carrier to transport coal.
Cnly very small amounts may be made into a colloid with
water9 and so made naturally stable for transportation."
(At lines 48-59 of page 1~
In May of 1957, when Clancey et. al. issued U.S. patent
2,791,471, this "critical value" was placed somewhat higher.
; At lines 13-19 of Column 2 of this patent, it is taught that
". . .coal at the slurry preparation terminal. . .is mixed
with water to form a slurry. . . .The resulting slurry should
contain about 35 to 55 percent coal by weight." A similar
disclosure appears in U.S. patent 2,791,472 of Barthauer
et. al., which also issue~ in May of 1957. At lines 45-49
of the Barthauer et. al. patent, it is disclosed that "Coal
selected for pipeline shipment is crushed to a suitable size
consist, screened and mixed with water to form the slurry
for transportation. The resulting slurry should contain about
35 to about 55 percent coal by weight."
In January of 1960 Wasp et. al. issued U.S. patent
2,920,923. In this patent, they discussed the prior art
Clancey et. al. process and stated that "Certain hydraulic
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principles relating to pipeline transportation have been set
forth in U.S. patent 2,971,471. A commercial pipeline,
embodying these hydraulic principles, has been constructed in
Ohio. . . .Ihis coal is mixed with an equal weight of water
to comprise a 50 percent aqueous coal slurry." (Lines 24-38
of Column 1)
In January of 1963, U.S. patent 3,073,652 was issued
to Reichl. Ihe Reichl patent appears to disclose that the
aforementioned "critical value" of solids content could be as
high as 60 weight percent. At lines 30-40 of column 1, it i5
stated that "The coal particles, that is both the fine and
coarse particles, are mixed with water to form a coal-water
slurry having a solids concentration of between 35 and 60
percent by weight coal particles. It has been discovered
that a slurry prepared as described above is dynamically stable
in that the tendency of the larger sized coal particles to
settle out of the slurry is reduced. . . ." However, as is
taught in the Cole et. al. patents, the coal concentrations
taught in Reichl appear to be calculated 011 a "wet basis"
and, thus, apparently correspond to "dry basis" coal
concentrations of up to about 45 weight percent.
In February of 1965, U.S. patent 3,168,350 was issued
to Phinney et. al. In the Phinney patent, reference is again
made to the prior art Clancey et. al. process disclosed in
U.S. 2,791,471. With regard to the prior art process, Phinney
et. al- stated that "The process employed to transport the coal
as an aqueous slurry through this commercial pipeline is set
forth in U.S. patent 2,791,471. . . .The coal particles having
the above size distribution and nominal top size are mixed
with water to prepare a slurry comprising 35-55 percent by
weight of the coal particles and the remainder water."
tLines 25-37 of column 1)
In December of 1976, a U.S. patent issued which disclosed
that, at above a solids content of 50 percent of coal (dry basis),
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a slurry i3 unp~mpable. U.S. patent 3,996,0Z6 of Cole disclosed
that "Ordinarily, a pumpable slurry of solid fuel or coal
requires the addition of water to the powdered fuel to form
a slurry containing not more than about from 40 to 45 wt. %
coal. As the solids content increases above this range the
slurry becomes increasingly difficult to pump and at about
50% solids content, it is unpumpable. ~at lines 29-36 of
column 1) Cole also teaches that the as-mined coal contains
a substantial amount of moisture and, unless it is dried, a
slurry containing 50 weight percent of such as-mined coal in
fact contains substantially less than 50 weight percent of
coal. At lines 37-47 of his patent, he discloses that
"Actually such slurries contain in excess of 50% water as
there is a considerable amount of water in coal as mined. . . .
The coal or solid fuel also contains chemically bound
water. . . .depending on the type of solid fuel, a p~mpable
slurry may contain as little as 30 to 35 wt. % solids on a
dry basis."
In May of 1978, yet another patent issued disclosing
that a pumpable coal-water slurry could contain no more than
about 40 to about 45 weight percent of coal. U.S. patent
4,088,453 disclosed that "The amount of water necessary to form
a pumpable slurry depends on the surface characteristics of
the solid fuel. . ~ .in the case of a slurry made up of
solid fuel particles most of which will pass through a 200 mesh
sieve it has been found that ordinarily, a pumpable slurry must
contain from 55 to 60 wt. % water." (Col~mn 1, lines 25-46)
In August of 1978, U.S. patent 4,094,035 issued to Cole
et. al. It also contained disclosure that a coal-water slurry
3~0 with more than 50 weight percent of coal was unpumpable; the
portion of U.S. patent 3,966,026 quoted hereinabove was
included verbatim in the Cole et. al. 4,104,035 patent.
The prior art also appears to disclose that the use of
more than about 50 weight percent of coal in a coal-oil
.26
mixture has an adverse effect upon the pumpability of the
mixture. Thus, e.g., U.S. patent 3,907,134 teaches that "The
fuel oil and particulate carbonaceous material are preferably
mixed in metered amounts.... For most users about 5 weight
percent of coal or less is not normally economically
interesting, and above 50 weight percent of pulverized coal
begins to cause undesirahle flow characteristics in the slurry"
(at lines 41-50 of column 1).
U.S. patent 3,846,087 discloses that, with regard to
carbon-oil slurries, "...major problems are encountered in
maintaining the carbon-oil slurry pumpable when the carbon
content thereof exceeds about 4 weight percent in naphtha, gas
oil, lube oil, shale oil, decanted oil, gasoline, crudes
deficient in + 1000F~ boiling material or in hydrocarbon
deficient in + 1000Fo bolling material. Above this figure,
the slurry does not flow and upon heating only becomes more
gel-like" (lines 8-15 of column 1).
In the prior art, it is recognized that liquid fuels must
be vaporized before they can be burned. Most large capacity
industrial burners use two steps to get liquid carbonaceous
fuel ~such as, e.g., oil) into combustible form--atomiæation
plus vaporization. Atomization is the process of breaking a
liquid into a multitude of tiny droplets. By first atomizing
the liquid carbonaceous fuel and thus e~posing the large
surface area of millions of tiny droplets to air and to heat,
atomizing burners are able to vaporize liquid carbonaceous fuel
at very high rates. See "North American Combustion Handbook",
Second Edition (North American Mfg. Co., Clevelar.d, Ohio.
1978), pages 251 and 418.
The prior art discloses that, in general, the viscosity
required for the effective atomization of a liquid carbonaceous
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fuel is substantially lower then the viscosity required to
effectively pump said fuel. Cn page 30 of the "North Qmerican
Combustion Handbook", supra, it is disclosed in Figure 2.8
that, for fuel oils, pumping should occur at a viscosity of
from about 5,000 to about 10,000 Saybolt '~conds Universal
(IISSUll)~ and easy pumping should occur at a viscosity of
from about 2,000 to about 5,000 Saybolt Seconds Universal.
However, atomization occurs within the range of from about 70
; to about 150 Saybolt Seconds Universal. Cn page 27 of said
"North American Combustion Handbook", in discussing said
Figure, it is stated that "Certain ranges of viscosity have
been found best for pumping and for atomization of fuel oils.
These ranges are shown as shaded areas on Figure 2.8."
In summary, the prior art teaches that carbonaceous
slurries containing more than about 50 weight percent of
carbonaceous material cannot be effectively atomized and
burned. In the first place, they cannot be pumped to the
atomi~er because, at solids contents of greater than about
50 weight percent, they are unpumpable. In the second place,
even when said slurries have a low enough viscosity to be
unpumpable, they often have too high a viscosity to be
effectively atomized and burned.
In accordance with this invention, there is provided
a process for combusting a carbonaceous ~lurry.
In the first step of this process, a stable, low
viscosity, carbonaceous slurry is provided. This slurry
contains a specified particle size distribution, contains at
least 5 weight percent of colloidal carbonaceous particles,
has a yield stress of from about 3 to about 18 Pascals, and
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lZ~9i;~6
is comprised of a carbonaceous consist which has an
interstitial porosity of less than about 20 volume percent and
a specific surface area of from about 0.8 to about 4.0 square
` meters per cubic centimeter. This slurry contains at least
about 55 volume percent of carbonaceous solids and preferably
has a specified interrelationsh:p between its solids content
and the porosity of said consist, the specific s~rface area of
said consist, and the zeta potential of the colloidal
carbonaceous particles in the consist. More details of the
slurry employed in the process of the invention are described
in the following disclosure.
In the second and third steps of this process, said slurry
is atomized and combusted.
In the description of the detalls of the process of the
invention, reference will be made to the accompanying drawings,
wherein:
Fig. 1 is a chart showing the correlation between the zeta
potential of coal particles in a fluid and the specific
conductance of the fluid as a function of percent dispersing
agent added to the fluid for two candidate dispersants;
Fig. 2 is a flow sheet of a preferred process for
preparing the slurry used in the burning process of this
invention;
Fig. 3 is a cross-sectional view of a typical atomizer, or
turbulent flow, burner in which said slurry can be burned; and
Fig. 4 is a cross-sectional view of an oil burner in which
the slurry used in the process of this invention can be burned.
The slurry used in the burning process of this
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invention can be prepared by several different means. In one
of the preferred means, a specified grinding mixture is used.
Said grinding mixture contains from about 60 to about 82
parts by volume of carbonaceous material, from about 18 to
about 40 parts by volume of carrier liquid, and from about
0.01 to about 4.0 parts, by weight of dry carbonaceous
material, of dispersing agent; the pH of this grinding
mixture is from about 5 to about 12.
The grinding mixture used can be
provided either prior to or during grinding. In one
embodiment, the carbonaceous material, carrier liquid,
and dispersant are mixed to provide the grinding mixture,
and the mixture so provided is then ground to produce a
stable slurry. The aforementioned materials can be mixed
by means well known to those skilled in the art i~cluding,
e.g., blending them together, grinding them together, and
combinations of blending and grinding them together. In
another embodiment, all of the carbonaceous material
desired in the grinding mixture is mixed with less than all
of the carrier liquid and/or dispersant desired in the
grinding mixture, and the incomplete mixture is then ground
while the remainder of the carrier liquid and/or the dispersant
is added during grinding; in this embodiment, the desired
grinding mixture is generated in situ during grinding. In
another embodiment, less than all of the carbonaceous material
desired in the grinding mixture is mixed with carrier liquid
and dispersant, and the incomplete mixture is then ground
while the remainder of the carbonaceous material is added
during grinding; in this embodiment, the desired grinding
mixture is also generated in situ during grinding. ~ther
embodiments will be apparent to those skilled in the art.
As used in this specification, the terms "mixed" and
"mixing" refer to the steps of combining or blending
several masses intG one mass and includes, e.g., blending,
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grinding, milling, and all other steps by which two or more
masses are brought into contact with each other and
combined to some extent. Conventional means for mixing
viscous materials can be used.
Ihus, by way of illustration and not limitation,
one can use batch mixers such as change-can mixers,
statior.ary tank mixers, gate mixers, shear-bar mixers,
helical blade mixers, double-arm kneading mixers, screw~
discharge batch mixers, intensive mixers, roll mills, bulk
blenders, ~ittleford-Lodige mixers, cone and screw mixers,
pan muller mixers, and the like; one can use continuous
mixers such as single-screw extruders, the Rietz extruder,
the Baker Perkins Ko-Kneader, the Transfer-Mix, the Baker
Perkins Rotofeed, twin-screw continuous m.ixers, trough
and screw mixers, pug mills, the Kneadermaster, and the
like.
In the process described in this specification, a mixture
comprising from about 60 to about 82 volume percent of one or more
solid carbonaceous materials ~such as, e.g., coke and/or coal)
and one or more carrier liquids (such as, e.g., water and/or
oil) is ground until a slurry with specified properties is
obtained. Said carbonaceous material/carrier liquid mixture
is hereinafter referred to in this specification as the
"grinding mixture".
The grinding mixture used
is preferably comprised of at least one carbonaceous solid
material. As used in this specification, the term
"carbonaceous" refers to a carbon-containing material and
includes, by way of illustration and not limitation, coal,
coke, graphite, charcoal, char, and the like. The preferred
carbonaceous materials are carbonaceous fuels.
In one preferred embodiment, the carbonaceous solid
is coal. By way of illustration, anthracite, semi-anthracite,
medium, and high-volatile bituminous, sub-bituminous and
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lignite coals may advantageously be used.
The coal for use in the process can be obtained
in a dry or wet form and mixed with fluid to form a coal-
fluid mixture. Preferably, the coal for making a fine
particle sized fraction is wet milled in known ways to
prevent dust and explosion hazards, while optionally
adding dispersing agent(s) to the fluid. The wet
milled coal fraction can be milled with all the water, or
it can be mixed with sufficient additional water to make a
slurry when it is further mixed with a coarser cr~shed
coal fraction.
In view of the manner in which coal fractures
during milling, coal particles will have irregular shapes
which, however, are of a body (or maximum side-to-side
thickness) such that the sub-sieve sized discrete particles
will pass through a specified mesh of a sieve. The size
of the discrete particle can be expressed in terms of a
spherical diameter which, as used herein, is defined as a
U.S. sieve size of from 4 mesh to 400 mesh (38 ~m)
through which a coal particle from a sample of coal or
coal-water slurry will pass. Eor particles finer than
200 mesh (74 ~m), the size of the particles can be
determined by means of a sieve, or a sedimentometer,
or a scanning electron microscope (SEM), or the like.
In one preferred embodiment, the carbonaceous
solid material is coke. Coke is the solid, cellular,
infusible material remaining after the carbonization
of coal, pitch, petroleum residues, and certain other
carbonaceous materials. The varieties of coke, other than
those from coal, generally are identified by prefixing a
word to indicate the source, e.g., "petroleum coke". To
indicate the process by which a coke is manufactured, a
prefix also is often used, e.g., "beehive coke".
High temperature coke can be used in this invention.
.,
26
As is known to those skilled in the art, this coke can
be prepared from bituminous coal. Most of this type of
coke is made in slot-type recovery ovens. In general,
this type of coke contains from about 0.6 to about 1.4
weight percent of volatile matter and has an apparent
specific gravity of from about 0.8 to about 0.99.
Foundry coke can also be used in this invention.
In general, the volatile matter in this type of coke i3
less than about 2 weight percent.
Low temperature coke and medium temperature coke
can also be used in this invention.
Pitch coke can be used in this invention. Pitch
coke is made from coal-tar pitch; it has about 1.0 percent
volatile matter, and it generally contains less than 0.5
percent sulfur.
Petroleum coke can be used in this invention. There
are at least two types of petroleum coke: delayed coke and
fluid coke. Delayed coke generally contains from about 8
to about 18 weight percent volatile matter, has a
grindability index of from about 40 to about 60, and has
a true density of from about 1.28 to about 1.42 grams per
milliliter. Fluid coke generally contains from about
3.7 to about 7.0 weight percent of volatile matter, has
a grindability index of from about 20 to about 30, and
has a true density of from about 1.5 to about 1.6 grams
per milliliter.
In another preferred embodiment, the carbonaceous
solid materia] is char. Char is the non-agglomerated,
non-fusible residue from the thermal treatment of solid
carbonaceous materials. Coal char i3 obtained as a
residue or a coproduct from low~temperature carbonization
processes; such a char typically contains from about
1 to about 5 weight percent of volatile matter.
In another preferred embodiment, the carbonaceous
1'~19~Z~
material i3 charcoal. Charcoal is the residue remaining
after the destructive distillation of wood.
In yet another embodiment, the carbonaceous material
is solvent refined coal.
In general, any carbonaceous fuel can be used as the
solid carbonaceous material in this invention.
Mixtures of carbonaceous solids also can be used. By way
of illustration and not limitation, one can use a mixture
of at least one coarse carbonaceous fraction which contains
less than about 30 weight percent of volatilizable hydrocarbons
(such as, e.g., anthracite or low volatile bituminous coal)
and at least one fine
carbonaceous fraction which contains more than about 35 weight
percent of volatilizable hydrocarbons (such as, e.g., lignite
or high volatile bituminous coal). Cne can use a mixture of
two or more of said coarse carbonaceous fractions and one of
said fine fractions, one of said coarse carbonaceous fractions
and two or more of said fine fractions, or two or more of
said coarse carbonaceous fractions and th~O or more of said
fine fractions. In this embodiment, the grinding mixture
is preferably comprised of from about 2 to about 50 weight
percent of solid carbonaceous material which has a median
particle size of from about 0.5 to about 40 microns and
from about 50 to about ~8 weight percent of solid
carbonaceous material which has a median particle size in
excess of 40 microns.
In one embodiment of this invention, the
grinding mixture is comprised of at least two
consists of carbonaceous material. As used in this specifi-
cation, and in the prior art, the term "consist" means theparticle size distribution of the solid phase of the
carbonaceous material/fluid slurry. For example, in the
prior art, the term "8 mesh x 0", when used with reference
to a coal-water slurry, indicates cGal with a graded size,
1~L91;~6
or consist, of coal particles distributed in the range of
8 mesh and zero, or 2360 microns x zero microns.
Similarly, the term "about 1180 microns x 0.05 microns"
indicates coal with a nominally measurable graded size,
or "consist", of coal particles distributed in the range
of from about 1180 microns to a measurable colloidal size,
e.g., at least about 0.05 microns. The term "about ~180
microns" is nominally equivalent to a U.S. Series 16 mesh
sieve, substantially as defined in "Handbook of Chemistry
0 and Physics", 54th Edition, 1973-1974, CRC Press, Cleveland,
Ohio, page 143, "Standard Test Sieves (wire cloth)".
Unless otherwise stated in this
specification, the weight of carbonaceous material is on a
moisture-free or "dry basis" herein. Thus, e.g., the
"solids" in as-mined carbonaceous material include, e.g.,
carbonaceous material and ash. Thus, there is a
considerable amount of bound water in coal as mined; the
volume of this water in the coal is not included in the
solids weight in order to calculate the volume percent
of "dry solids" in the grinding mixture used in the process
of this invention. Thus, as used herein, the term "dry
basis" refers to coal (and/or other carbonaceous materialj
which is substantially free of carrier liquid. Carbonaceous
material is considered to be dry after it has been air dried
by being exposed to air at a temperature of at least
70 degrees Fahrenheit and a relative humidity of less than
humidity of less than 50 percent for at least 24 hours.
In a preferred embodiment,
at least two consists of carbonaceous material are
mixed with carrier fluid to prepare the grinding mixture.
Both of said consists of
carbonaceous material can be produced by wet grinding;
thus, e.g., one of the consists can be produced by grinding
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coal at a high solids content (60-82 volume percent) in
the presence of water and optionally, surfactant, the second of
the consists can be produced by grinding coal at a lower solids
content (30-60 volume percent) in a ball mill or a stirred
ball mill, and the first and the second coal consists can be
ground together with each other (and, optionally, with one
or more additional consists produced by wet and/or dry
grindil1g) at a solids content of from about 60 to about 82
volume percent in the optional presence of from about 0.01
to about 4.0 weight percent of dispersant and water.
Alternatively, both of said consists
of carbonaceous material can be produced by dry grinding;
thus, e.g., one of the consists can be prepared by grinding
one pulverized coal (i.e., coal which has been milled
or ground to a consist of about 20 mesh by 0) in, e.g., a
ring roller mill, a second or more of the consists can be
prepared by dry grinding a second pulverized coal in, e.g.,
a micronizer fluid energy (jet) mill, and the two ground dry
fractions are then blended in a blending tank at a solids con-
centration of from 60-90 volume percent with water and, optionally,
0.01 to 4.0 weight percent of dispersant at a high shear stress in
a mixer such as Greerco in-line mixer.
Alternatively, at least one of said consists can be
produced by wet grinding, and at least one of said consists
can be produced by dry grinding; thus, e.g., one of the
consists can be produced by wet grinding coal at a low
solids content (30-60 volume percent) in the presence of
water and, optionally, dispersant, a second of the consists
can be produced by dry grinding pulverized coal in either a
micronizer fluid energy (jet) mill, or a ring roller mill,
and the consists produced by wet and dry grinding are then
blended in a blending tank at a solids concentration of
60-82 volume percent water and, optionally, 0.01 to 4.0 weight
percent of dispersant at a high shear stress in a mixer such
~Z~9126
as a Greerco in-line mixer.
Alternatively, one can prepare the grinding mixture
by wet grinding (or regrinding~ slurry
comprised of carbonaceous material to prod~ce the fine
consist for the mixture. Thus, by way of illustration,
a fine consist can be prepared by regrinding a "final
slurry" product at a concentration of from about 40 to
;~ about 60 weight percent solids (and preferably at from
; about 45 to about 55 weight percent of solids) in, e.g.,
a stirred ball mill until slurry is from about 4 to about
20 microns. The coarse consist can be produced by dry
j crushing ~in, e.g.~ a roll crusher, a gyratory crusher,
a cage mill, etc.) the carbonaceous material to a nominal
3/8" x 0 size so that the median particle size of the
coarse fraction exceeds 40 microns. The coarse and fine
fractions can then be combined with each other, carrier
liquid, and dispersing agent to produce a grinding
mixture comprised of from about 60 to about ~2 volume
percent of carbonaceous material, from about 18 to about
40 volume percent of carrier liquid, and from about 0.01 to
about 4.0 weight percent of dispersing agent.
The fine consist in this particular embodiment can
alternatively be made by regrinding a dry pulverized coal
at a concentration of from about 40 to about 60 weight percent
to produce a consist with a median particle size of
from about 4 to about 20 microns.
T~le aforementioned processes are all illustrated
in Figure 2.
It will be apparent to those skilled in the art that
there are many other arrangements wherein two consists of
carbonaceous material can be mixed with carrier liquid to
produce the grinding mixture of this invention.
The solid carbonaceous material in the
grinding mixture preferably consists essentially of
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1~9P~6
at least one fine 301id carbonaceous material and at least one
coarse solid carbonaceous material.
From about 2 to about 50 weight percent of the solid
carbonaceous material in the grinding mixture is comprised
of fine solid carbonaceous material with a median particle
size of from about 0.5 to about 40 microns; it is preferred
that from about 4 to about 40 weight percent of the solid
carbonaceous material in the grinding mixture be comprised
of fine solid carbonaceous material with a median particle
size of from about 1 to about 30 microns; and it is even more
preferred that from about 6 to about 30 weight percent of
the solid carbonaceous material in the grinding mixture be
comprised of fine solid carbonaceous material with a median
particle size of from about 2 to about 20 microns. From
about 50 to about 98 weight percent of the solid
carbonaceous material in the grinding mixture is comprised
of coarse solid carbonaceous material with a median particle
size greater than 40 microns.
The grinding mixture can contain one fine carbonaceous
solid fraction or several fine carbonaceous solid fractions,
which may be the same or different carbonaceous materials;
regardless of whether one or several such fine fractions
are present in the grinding mixture, from about 2 to about
50 weight percent of the solid carbonaceous material in
the grinding mixture has a median particle size of from
about 0.5 to about 40 microns~
The grinding mixture can contain one coarse
carbonaceous solid fraction or several coarse
carbonaceous solid fractions, which may be the same or
different carbonaceous materials; regardless of whether
one or several such coarse fractions are present in the
grinding mixture, from about 50 to about 98 weight
percent of the solid carbonaceous material in the grinding
mixture has a median particle size greater than about
16
9~26
40 microns. It is preferred that the grinding mixture
be comprised of from about 60 to about 96 weight percent
of said coarse solid carbonaceous material, and it is
more preferred that said grinding mixture be comprised
of from about 70 to about 94 weight percent of said
coarse solid carbonaceous material.
The grinding mixture can be comprised of discrete fine
; fraction(s) and coarse fraction(s) of solid carbonaceous
material. Alternatively, the grinding mixture can be
comprised of a single fraction of carbonaceous material,
which was produced by mixing said coarse fraction(s) and
said fine fraction(s). As long
as a particle size analysis of the solid cabonaceous material
in the grinding mixture reveals that from about 2 to
about 50 weight percent of said material has a median
particle size of from about 0.5 to about 40 microns, and that
from about 2 to about 50 weight percent of said material
has a ~edian particle size greater than 40 microns, then
the consists of carbonaceous material are
suitable for use in the grinding mixture of this
invention. The particle size analysis of the carbonaceous
material will show substantial undulation at one or more
points in the entire CPFT plot where two or more size
distributions have obviously merged.
The carbonaceous solid is preferably mixed with from about
0.01 to about 4.0 weight percent (based upon dry weight of
carbonaceous solid) of dispersing agent to produce said grinding
mixture. In the case where at least two consists of carbonaceous
solid material are mixed with liquid, (1) both
Of the consists can be dry ground and mixed with liquid
and dispersant, (2) the dispersant can be mixed with the
liquid, and the dry ground consists can be mixed with the
liquid-dispersant mixture; (3) one of the consists can be
dry ground, a second of the consists can be wet ground with
~z~9~26
part or all of the dispersant, and the ground consists can
be mixed with the balance of the liquid and dispersant
which was not theretofore mixed with the consists, or (4)
some or all of the dispersant can be wet ground with one
or both of the consists, and the ground consists can then
be mixed with the liquid and the balance of the dispersant
which was not theretofore mixed with the consists; (5) one
or more consists can be wet ground with no dispersant and
insufficient total water and then blended with dispersant
and the balance of the water and/or other consist blends.
The grinding mixture used contains from about 60 to about
82 volume percent of one or more carbonaceous solid materials.
It is preferred that said grinding mixture contain from about
64 to about 81 volume percent of said carbonaceous solid
material. In a more preferred embodiment, the grinding
mixture contains from about 75 to about 80 volume percent
of said solid carbonaceous material.
The grinding mixture generally has a pH of from about 5 to
about 12. It is preferred that the pH of the grinding mixture be
from about 7 to about 11.
Ihe grinding mixture is comprised of one or more liquids.
As used in this specification, the term liquid
refers to a substance which undergoes continuous deformation
under a shearing stress. The liquid used in the grinding
mixture preferably performs at least
two functions -- it fills the interstitial pores of the
carbonaceous solid material, and it provides the vehicle
for separation of the particles of the carbonaceous solid
material to minimize collisions between said particles;
thus, the preferred liquid is a carrier liquid.
By way of illustration and not limitation, some
of the liquids which can be used in the slurry
include water; waste industrial solvents such
as, e.g., effluents from waste disposal plants, contaminated
12~9~2~;
waste water containing hydrocarbons from e.g., oil-3eparation
processes~ and the like; aromatic and aliphatic alcohols
containing 1-10 carbon atoms, such as methanol, propanol, ethanol,
butanol, phenol, mixtures thereof, and the like; pine oil; petroleum
liquid3 such as, e.g., number ? fuel oil, number 4 fuel oil,
number 6 fuel oil, gasoline, naphtha, mixtures thereof, and the
like; hydrocarbon solvents such as, e.g., benzene, toluene,
xylene, kerosene, and derivatives thereof; acetone; aniline;
anisole; halobenzenes such as; e.g., bromobenzene and
chlorobenzene; nitrobenzene; carbon tetrachloride; chloro-
form; cyclohexane; n-decane; dodecane; 1,1,2,2-tetrachloroe-
thane; ethyl bromide; 1,2-dichloroethylene; tetrachloro-
ethylene; trichloroethylene; ethylene chloride; ethyl ether;
ethyl iodide; glycol; n-hendecane; n-heptane; 1-heptanol;
1-hexanol; methylene halides such as, e.g., methylene
chlori~e, methylene bromide, and methylene iodide; n-octa-
decane; n-octane; 1-octanol; n-pentadecane pentanol; and
the like. The aforementioned list is merely illustrative,
and those skilled in the art will recognize that many other
liquids can be used.
In one preferred embodiment, the liquid used
is carrier water. As used in this
specification, the term "carrier water" means the bulk of
free water dispersed between the carbonaceous particles and
contiguous to the bound layers on the particles, and it is to be
distinguished from bound water. ~he term "bound water'~
means water retained in the "bound water layer", as defined
and illustrated in Kirk-Othmer, Encyclopedia of Chemical
Technology, 2d Edition, Vol. 22, pages 90-97 tat p. 91).
When the liquid mixed with the carbonaceous solid is
water or is comprised of from about 5 to about 99 weight
percent of water, it is preferred that the temperature
of the solids-liquid mixture be maintained at from ambient
to about 99 degrees centigrade during mixing to insure that
19
~2~126
the water does not substantially vaporize.
When water is added to a carbonaceous powder comprised
of finely divided particles, and if the water "wets"
the powder, a surface water film is adsorbed on each
particle which i~ known to be structurally different from
the surrounding "free" or bulk water, in that the film
may be described as "semi-rigid", or "bound water film".
Depending on the fundamental electrical potential of the
surface, this "semi-rigid" or bound water film may be of
several molecules thickness.
Mixtures of at least two liquids can be used in the grinding
mixture. Thus~ by way of illustration
and not limitation, one may use mixtures of water and
ethanol, water and petroleum liquids~ and the like.
Cne can use mixtures comprised of from about 1 to about 99
volume percent of alcohol and from about 99 to about
1 volume percent of water. In one preferred embodiment,
the mixture is comprised of from about 1 to about 15
volume percent of alcohol with the remainder of the liquid
consisting essentially of water. It is preferred that the
alcohol be liquid and monohydric and that it contain from
about 1 to about 10 carbon atoms. Suitable monohydric
alcohols are listed on page 265 of Fieser and Fieser's
"Advanced Organic Chemistry" (Reinhold, N.Y., 1961).
In one preferred embodiment, the grinding mixture
is comprised of at least about 60 volume percent of
carbonaceous solid material and from about 18 to about
40 volume percent of carrier liquid. In one aspect of
thi3 embodiment, at least about 90 weight percent of the
carrier liquid is water and less than about 10 weight
percent of the carrier liquid is petroleum liquid. In
this aspect, it is preferred that the petroleum liquid be
' - 20
~2~9~26
selected from the group consisting of naphtha, high gas
oil, low gas oil, catalytic cracked recycle oil, mixtures
thereof, and other similar petroleum products. Vegetable
oils such as corn, bean, or pine oil may also be used to
replace part or all of the petroleum liquid.
Ihe grinding mixture is comprised of
from about 18 to about 40 volume percent of one or more
carrier liquids. It is preferred that the grinding mixture
contain from about 19 to about 36 volume percent of one
or more carrier liquids. In the most preferred embodiment,
the grinding mixture is comprised of
from 20 to about 25 volume percent of one or more carrier
liquids.
In addition to the aforementioned carbonaceous solids,
carrier liquid(s), and dispersant, the grinding mixture also can
contain from about 0 to about 10 volume percent of other additives
sometimes present in coal-water slurries such as, eOg.,
inorganic electrolytes, etc.
The grinding mixture contains from about 0.01 to about 4.0
weight percent of dispersing agent, based upon the
weight of dry carbonaceous solid material. The grinding
mixture can contain the amount and type of dispersing
agent which is most effective for it. Means for determining
the identity and amount of the most effective dispersing
agent for a given mixture will be described below for a
coal-water mixture, it being understood that the technique
described is applicable to other mixtures such as, e.g.,
coke-water, graphite-water, etc.
In general, for any given system, the
identity of effective dispersing agents can be determined
by measuring the effects of the disperant upon the system
at a given dispersant concentration; viscosity versus
shear rate of the stirred coal-water slurry is measured
while titrating with increasing amounts of the dispersing
12~ L2~
agent, and the po1nt at which the alurry vi3c03ity cea~e~
to decrease i~ noted. For any given di3per~ant~), and
system, the mo~t effective concentration i~ the
one which give3 the minimum v~co~ity under a given set
of te3t condition3, and the efficiency of different
dispersant3 can be compared by te3ting them with a given
sy~t~m under comparable concentration and te3t condition3.
Thu3, for example, one can dry grind a 3ample of cval in
a laboratory 3ize ball mill with porcelain or steel ball~
in water at 50 weight percent ~olid3, e.g., for 24 hour3
or until all of the particle~ in the coal are le~ than
10 microns in ize; other grinding devices known to tho3e
skilled in the art may al~o be used such a3 vibroenergy
mills, 3tirred ball mill3, or fluid energy mill3. Small
3amples (about 500 milliliter3 apiece) of the 3y3tem can
then be deflocculated by adding vario w di3per3ing agent~
to the amples dry or preferably in ~olution dropwi e,
blending the mixture at any con3i3tent bler~ing energy
(which may be gentle as mixing by hand, or at very high
shear energy which will improve di~persion), and then
mea~uring the vi3c03ity at 30me constant ~hear rate by,
e.g., u3ing a Erookfield RVT vi3cometer at tO0 revolution3
per minute. The di~per31ng agent (or combination of
di~per~ing agent3) which i3 found to produce the lowe3t
vi~cosity for the ~y3tem at a given shear rate and di3per~ing
agent(3) concentration i~ the moat effective for tho3e
condition~. Ihi3 technique i3 deqcribed in detail in my
U.S~ patent 4,282,006.
_ Figure 1 illu~trate~ one mean3 of evaluating
the effectivene3~ of 3urfactant3 for any given ~olid
material. The curve3 of Fig. 1 represent data obtained
u3ing both a purported nonionic polymer CW-11*made by the
Dlamond Shamrock Proce33 Chemical3 Co. and an anionic
* Trademark
~.Z~ 6
lignosulfonate Polyfon-~ made by Westvaco, Inc.
adsorbed on an Australian coal. The fine coal ground to
about 100% finer than 10 microns is slurried in distilled
water at 0.01 weight percent solids. Aliquots are placed
in test tuhes and increasing ~mount~ of any candidate
surfactant i3 added to each te~t tube. The teAt tube
samples are thoroughly mixed and inserted into a sampler
carousel. The Pen Kem System 3000 Electrophoretic Mbbility
Analyzer automatically and sequentially sample3 each te~t
tube and measures the electrophoretic mobility of the coal
particle~ and the specific conductance of the carrier liquid.
pH can al~o be mea3ured on each ~ample. In Fig. 1 the left
ordinate give3 the calculated zeta potential of the particle~
in millivolt3, the right ordinate gives the specific conductance
- 15 in micromhos of the carrier liquid. The~e variables are
both measured as a function of the percent addition of each
surfactant on a dry coal ba3i3 which is plotted on the
abscis3a. ~igure 1 show3 that the purported nonionic CW-11
surfactant does have some anionic character. CW-11 ha~ a
zeta potential of -50 mv at 300X addition 0.01% dry coal.
Pblyfon-F ha3 a zeta potential of -55 mv at 200% addition
on 0.01% dry coal. Furthermore, the specific conductance
of the Polyfon-F at -55 m.v. zeta potential is greater than
CW-ll at -5Q m.v. These data establish Polyfon-~ as a more
chemically effective surfactant for use on thiq particular
Australian co~l.
The amount of di3persing agents used will vary,
depending upon such factor3 a~ the concentration of
the carbonaceous materlal in the ilurry, the particle size and
particle size distribution, the amount of a3h minerals (i.e. clays
and other minerals present), the temperature of the slurry,
the pH, the original zeta potential of the
particles, and the identity of the di3persing agentt ) and
its concentration. In general, the di~persing agent is present
* - Trademark
- 23
l.Z~9~26
in the slurry, at from 0.01 to 4.0 weight percent based on
the weieht of dry carbonaceous materia~. Procedurally, in
determining the amount of a specific dispersing agent needed,
a series of measurements can be made of visco3itie3 versu3 shear
rates versu3 zeta potential for a series of solids-liquid slurries
containing a range of amounts of a particular dispersing agent
for a constant amount of solids-liquid slurry. The data can
be plotted and used as a guide to the optimum quantities of
that agent to use to obtain near maximum or ma~imum zeta
potential for that system. The coordinate of the
chart at which the visc03ity and/or zeta potential is not
changed significantly by adding more agent is selected as an
indication of the optimum quantity at maximum zeta potential,
and the amount is read from the base line of the chart.
lhe visc03ity and amount read from the titration chart is
then compared with an equivalent chart showing a correla-
tion among visc03ity, amount, and maximum zeta potential.
An amount of electrolyte and/or dispersing agent(s)
required to provide a maximum or near maximum zeta potential
and a selected visc03ity can then be used to make a
solid3-liquid slurry.
It is preferred that the slurry be compri3ed of an
amount of dispersing agent effective to maintain the particles
of material in dispersed form in the carrier liquid of the
slurry, to generate a yield stress in the slurry of from about
3 to about 18 Pascal3, and to charge the colloidal coal
particles in the slurry to a net zeta potential of from about
15 to about 85 millivolts. It is preferred that the slurry of
this invention contain from about 0.01 to about 4.0 percent, based
on weight of dry solids, of at least one dispersing agent. It
is more preferred that the slurry contain from about 0.03 to about
1.~ percent, based on weight of dry solids, of dispersing agent.
In an even more preferred embodiment, the slurry contains
from about 0.05 to about 1.4 percent, by weight of dry solids,
24
26
of dispersing agent. In the most preferred embodiment, the
slurry contains from about 0.l0 to about 1.2 percent of
dispersing agent.
It should be noted, however, that the use of the
s optimum amount of dispersing agent~s) does not, in and of
itself, guarantee that the slurry system will have dynamic
stability. Other factors, such as the slurry's specific
surface, porosity, and its solids content, must also be
taken into consideration, and these factors should be
interrelated in the manner specified in this specification.
It is preferred that the dispersing agent used
be an organic compound which
encompasses in the same molecule two dissimilar structural
groups, e.g., a water soluble moiety, and a water insoluble
moiety- It is preferred that said dispersing agent be a
surfactant. The term "surface-active agent", or "surfactant",
as used herein indicates any substance that alters
energy relationships at interfaces, and, in particular, a
synthetic or natural organic compound displaying surface
activity including wetting agents, detergents, penetrants,
spreaders, dispersing agents, foaming agents, etc.
~ he surfactant used is preferably
an organic surfactant selected from the group consisting
of anionic surfactants, non ionic surfactants, cationic
surfactants, and amphoteric surfactants. It is preferred that
the surfactant be either anionic or cationic. In the most
preferred embodiment, the surfactant is anionic.
It is preferred that the mclecular weight of the
surfactant used be at
least about 200. As used herein, the term "molecular
weight" refers to the sum of the atomic weights of all
the atoms in a molecule.
In one preferred embodiment, the surfactant is
anionic and its solubilizing group(s) is selected from
1~9126
the group consisting of a carboxylate group, a sulfonate
group, a sulfate group, a phosphate group, and mixture~
thereof. By way of illustration, one of these preferred
anionic surfactants is a polyacrylate having the general
formula
~----C C -
~ I .'
C- ~ .
1 .
OM
. _ _ n
wherein n is a whole number of at least 3 and M i3 selected
from the group consisting of hydrogen, sodium, potassium,
and ammonium.
In another preferred embodiment, the ~urfactant
is cationic and its solubilizing group(s) is selected from
the group consisting of a primary amine group, a secondary
amine group, a tertiary amine group, a quaternary ammonium
group and mixtures thereof.
In yet another embodiment, the surfactant is
amphoteric. In this embodiment, the surfactant has at
least one solubilizing group selected from the group
consisting of a carboxylate group, a sulfonate group, a
sulfate group, a phosphate group, and mixtures thereof;
and the surfactant also has at least one solubilizing
group selected from the group consisting of a primary
amine group, a secondary amine group, a tertiary amine
group, a quaternary ammonium group, and mixtures thereof.
In one of the more preferred embodiments, the
surfactant used is comprised
of at least about 85 weight percent of a structural
unit of the formula:
26
912~
(~b ~R, la
'~J
(X3)c (X2)d
whereln R1 and R2 are independently selected from the
group consisting of alkyl of from about 1 to about 6
carbon atoms and hydrogen; a, b, c, and d are integers
independently selected from the group consisting of
O, 1, 2, 3, 4, 5, 6, 7, and 8, and X2 and X3 are lnde-
pendently selected ~rom the group consi~ting of a
carboxylate group, a sulfonate group, a sulfate group, a
phosphate group, a nitro group, a halo group selected from
the group consisting of chloro, bromo, fluoro, and iodo,
--CN, an alkoxy group containing from 1 to about 6 carbon
atoms, and a group of the formula -R3 OR4 wherein R3
and R4 are an alkyl containing from about 1 to about 3
carbon atoms. The starting materials which can be used
to prepare these surfactants are well known to those
skilled in the art and include, e.g., naphthalene - o~
sulfonic acid (dihydrate)~ naphthalene-~-sulfonic acid
(monohydrate), ~-nitronaphthalene,~ -nitronaphthalene,
~-naphthylamine, ~ -naphthylamine, ~-naphthol, ~
naphthol, ~-naphthoic acid, ~ -naphthoic acid, ~-chloro-
- 20 naphthalene, ~-bromonaphthalene, ~ -bromonaphthalene, ~ -
chloronaphthalene, ~ -naphthonitrile, ~ -naphthonitrile,
1,5-dinitronaphthalene, 1,8-dinitronaphthalene, ~ -
methylnaphthalene, 1-nitro-2-methylnaphthalene, 2-
methylnapthalene-6-sulfonic acid, 2,6-dimethylnaphthalene,
~ -6-methylnaphtholpropionic acid, 1,6-dibromo-2-naphthol,
.2~
6-bromo-2-naphthol, 1,6-dibromonaphthalene, 6-bromo-2-
naphthol, and the like. Again, it is preferred that at
least one of the atoms in this surfactant be an alkali
metal selected from the group consisting of sodium,
potassium, ammonium, and mixtures thereof. One of the most
preferred surfactants from this group is the akali metal
salt of a condensed mono maphthalene sulfonic acid. This
acid, whose preparation is described in U.S. Patent 3,067,243,
can be prepared by sulfonating
naphthalene with sulfuric acid, condensing the sulfonated
naphthalene with formaldehyde, and then neutralizinæ
the condensate so obtained with sodium hydroxide. This
alkali or NH4+ metal salt of a condensed mono naphthalene
sulfonic acid is comprised of at least about 85 weight
percent of a repeating structural unit of the formula
,~,D~
( SO3M )a
wherein M i~ an alkali metal selected from the group
consisting of sodium, potassium, and ammonium and a is an
integer of from 1 to 8. Gomparable compounds with a
benzene rather than napthalene nucleus also can be used.
Examples of anionic organic surfactants which
have been found particularly advantageous are also
described below. In some cases, mixtures of two or more
of these surfactants beneficially can be used.
Sbme of the surfactants sold by the Dlamond Shamrock
Chemical Company of Mbrristown, New Jersey can be used in
this invention. Thus, by way of example, one can use
~, - 28
Z~,V~2~ ~
surfactant3 such as Lomar D (the sodium salt of a condensed
mono naphthalene sulfonic acid), Lamar*PW (sodium neutralized
naphthalene sulfonic acid), Lomar PWA (ammonia salt of a
condensed ~ono naphthalene sulfonic acid), A23* Nopcosperse*
YFG (condensed alkyl naphthalene sulfonate), and NopcoYperse
VEO (polymerized alkyl naphthalene sulfonate).
Some of the ~urfactantA sold by the R.T. Vanderbilt
Company of Norwalk, Connecticut can be used in this
invention. Thus, by way of example, one can use Darvan*~1
t odium naphthalene sulfonic acid formaldehyde), Darvan #2
(sodium salt3 of polymerized sub3tituted benzoid alkyl sulronic
acid~), and Darvan #6 (30dium salt3 of polymerized alkyl
naphthalene 3ulfonic acid).
Some of the 3urfactant3 301d by the We3tvaco-
Polychemicals, Charle~ton Height3, South Carolina can beuied in thi~ invention. Thu~, for example, one can u3e
Reax*~8B (sodium salt of a chemically modified low molecular
weight kraft lignin polymer solubilized by 4 ~ulfonate group3),
Reax 15B (~odium salt of 3ulfonated modified kraft lignin),
Reax 100M (reaction product o~ selected modified kraft
lignin~ with a high 3ul~0nic acid group content), and
Polyfon O (Augar-free, 3od1um-ba3ed ~ulfonate3 of Kraft
lignin).
~ome of the Aurfactant3 sold by the WR Grace ~ Co.,
Organic ChemicalA Div., Lexington, ffline can be used in thi3
invention. Thus, by way of illustration, one can u3e
Daxa~*ll, 11G, 15, or 19 (scdium 3alt3 of polymerized alkyl
naphthalene 3ui~0nlc acids~, Dbxad 30 or 31 (sodium salt of
a carboxylated polyelectrolyte), or Daxad 32 (ammonium salt
of a carb~xylated polyelectrolyte).
5ome of the ~urfactant~ sold by the Rohm ~ Haa3 Company
of Fhiladelphia, Penn3ylvania can be used in this invention.
Thus, for example, one can use, Triton*X-100 (octylphenoxy
polyethoxy ethanol), Triton N-101 (nonylphenoxy polyethoxy
* Trademarks
- 29
i6
ethanol), Tamol*731 (30dium salt of polymeric carboxylic
acid), Tamol 850 (sodium salt of polymeric carboxylic acid),
and Tamol SN (scdium ~alt of condensed naphthalene ~ulfonic
acid).
Some of the ~urfactants produced by the Hamblet
Haye~ Co. of Salem, Mb~achusetta can be used in this
invention. mu3, e.g., one can u3e Tek Tan NG*(oondensed
naptholene sulfonate).
Some of the 3urfactant3 made by the National Starch and
Chemical Corp. of Bridgewater, New JerQey can be u3e~ in
this invention. ThUQ, one can u3e Ver3a TL ~0 (an anlonic
polyeleetrolyte of 30dium polystyrene).
~ ome of the surfactant~ made by the Thompson-Hayward
Chemical Co. of Kansa3 City, Kansa~ also can be u~ed in thi3
invention. Thus, for example, one can we T-DEr*N-100
(nonylphenol-100 mole ethylene oxide adduct), T-DET N-50
(nonylphenol-50 mole ethylene oxide adduct), T-DET N-14
(~onylphenol-14 mole ethylene oxide adduct), T-DET N-9.5
(nonylphenol-9.5 mole ethylene oxide adduct), T-DET C-40
(polyethoxylated ca~tor oil with 40 les of ethylene oxide),
and the like.
Renex*30, a polyoxyethylene (12) tridecyl ether
manufactured by the ICI Corp. of Wilmington, Deleware, also
can be uaed in thi~ invention.
Some of the Dupanol*3urfactant3 manuf~ctured by the
E.I. duPont De Nemours ~ Co. of Wilmington, Deleware also
can be u9ed in this invention. Thus, one can u3e Dupanol WA
and Dupanol WAQ (both sodium lauryl 3ulfate~.
Some of the surfactant3 made by the Scher Chemicai~, Inc.
0 of Clifton, New Jer~ey al30 can be u~ed in thi3 invention.
Thu3, one can use cocamidopropyl betaine.
One cla3s of ~urfactants which can be u3ed in thi3
invention are the polyalkyleneoxide nonionic surfactants
having a hydrophobic portion and a hydrophilic portion,
* Tradema~ks
-- 30
~2~91.Z6
wherein the hydrophilic portion comprises at least about
100 units of ethylene o%ide. These surfactants are disclosed
in U.S. patent 4,358,293.
~he polyalkyleneoxide nonionic surfactants suitable for
use in the invention include the glycol ether~ of alkylated
phenol~ having a molecular weight of at least about 4,000
of the general formula:
~'
~ R ~ 0 ~ (CH2CH2C)N CH2 CH2
.
wherein R is substituted or unsubstituted alkyl of from 1.to 18
lO carbon atom~, preferabLy 9 carbon atoms; substituted or
unsubstituted aryl, or an amino group, and n i~ an integer of
at least about 100. The substituent~ of the alkyl and aryl
radicals can include halogen, hydroxy, and the like.
Cther suitable nonionic surfactant~ are the poly(oxyethylene)-
: 1~ poly(oxypropylene)-poly(oxyethylene) or as otherwise described
propoxylated, ethoxylated propylene glycol nonionic surfactant
block polymers having a molecular weight of at least about
- 6,000 of the general formula:
( 2 H2o)a~cH(cH3)cH2o]b~cH2cH2o) H
wherein a, b and c are whole integers and wherein a and c total
at least about 100.
Still other polyaikyleneox~de nonionic surfactants
; suitable for use in the invention are the block polymers of
: 25
'~7 - 31 -
1~9~Z~;
ethylene and propylene oxide derived from nitrogen-containing
compositions such as ethylene diamine and having a molecular
weight of at least about 14,000 of the general formula:
H~C~H4)e(-R2)a (R20-) (C2H40~ H
H(C2H40)f ( OR2)b (R20-)d(C2H40)hH
wherein R1 is an alkylene radical having 2 to 5 carbon atoms
preferably 2; R2 is alkylene radical having 3 to 5 carbon
atoms, preferably 3; a, b, c, d, e, f, g and h are whole
integers; and e, f, g and h total at least about 100.
One of the preferred surfactants is
H--~ ~.
~ i
' i=
o~
n
wherein M i~ alkali metal (and most preferably is sodium)
and n is le3s than 200 and, preferably, less than lOO.
While, in one embodiment, the use of the sodium,
potassium, or ammonium salts of condensed mononaphthalene
sulfonic acid is preferred, it is to be understood that the
3L.'Z~91~;
condensed mononaphthalene sulfonic acid can be used with
; the addition of sodi~m, potassium, or ammonium alkali to
form the corresponding alkali metal salt of that acid in
situ.
~ 5 Yet another of the surfactants which can be used in this
; invention is an anionic, alkylaryl sulfonate which is liquid
and has an HLB number of from about 8.0 to about 15Ø
Yet another preferred surfactant is a lignin-
based dispersing agent which i3 water soluble and which
o contains a sulfite lignin which ranges in molecular weight
from about 1,000 to about 50,000 and whose basic lignin
unit is a substituted phenylpropane. This lignin can be
generated by the acid sulfite wood pulping process.
Yet another preferred surfactant is a lignin-
bas~d dispersing agent which is water-soluble and which
contains an alkali lignin isolated from sulfate pulping
black liquor generated in the alkaline sulfate wood
pulping process.
Yet another cl~ss of preferred surfactan~ is
a complex polymerized organic salt of sulfonic acids of
the alkylaryl type such as, e.g., sodium naphthalene sul-
fonic acid formaldehyde,
Another preferred class of surfactants is the
lignosulfonates. These lignosulfonates have an equivalent
weight of from about 100 to about 350, contain from
about ~ to about 60 phenyl propane units (and, preferably,
from about 3 to 50 phenyl propane units), and are made up
of cross-linked polyaromatic chains. Some of the
preferred lignosulfonates include those listed
on page 293 of McCutcheon's "Emulsifiers and Detergents),
North American Edition (McCutcheon Division, MC Publishing
Co., Glen Rock, N.J~, 1981) and in the other portions of
McCutcheon's which describes said lignosulfonates.
- 33 -
~,1
21~
In one preferred embodiment, the lignosul-
fonate surfactant contains from about 0.5 to about 8.0
sulfonate group3. In this preferred embodiment 5 one species
has 0.5 sulfonate groups, one has one 3ulfonate group, one
has two sulfonate groups, and one has four sulfonate groups,
and one has 7.5 sulfonate groups.
Applicant does not wish to be bound to any particular
theory. However, he believes that a dispersing agent
in a aqueous slurry system might perform at least
three functions. In the first place, it is believed that a
water soluble dispersing agent, which also serves as
a wetting agent (such as an organic surfactant), functions
to promote the wettability of the carbonaceous particles by
water. As used herein, the term "wetting" indicates covering
or penetrating the carbonaceous particle surface with a bound
water layer. Such a wetting agent might or might not be needed,
depending upon the surface chemistry of the particle, its
hydrophobicity, and the associated electrochemistry of its
inherent bound water layers. For example, inherent bed
moisture, oxidation state of the particle, and chemical
compounds already present in natural carbonaceous deposits
may allow wetting of the ground material by added water.
In the second place, a dispersing agent might function
to promote deflocculation of carbonaceous particles, preferably
in the presence of advantageous electrolytes. As used
herein, the term "deflocculating" indicates di3persion of
particles, preferably of colloidal sized carbonaceous particles.
Thus, e.g., a "deflocculating agent" includes a dispersing
agent which promotes formation of a colloidal di3persion
of colloidal sized particles in a solids-liquid slurry. It
has been found that the presence of large, monovalent
cations - such as Na+, Li+, or K+ - tend to promote defloccu-
lation of colloidal sized carbonaceous particles in a solids-
liquid slurry. However, higher valence cations -- such as Ca+2,
A
- 34 -
~gl2~
Al+3, and Mg+2-- tend to cause said particles to flocculate
under certain conditions. Consequently, an organic anionic
surfactant which wets the carbonaceous particles and contains a
residual Na+ and/or K+ and an Li+ can be a very effective
5 deflocculant for the slurry.
In the third place, in some cases the dispersing
agent enhances the pumpability of the system~ It
is believed that this effect occurs because of enhancement
or inhibition of the bound, or semi-rigid, water layer be-
cause the dispersing agent provides a cation as a counterionfor the bound water layer, thereby affecting the yield pseudo-
plastic index (slope of a plot of log viscosity versus log
shear rate) of the mass. Preferably, the cation provided by
the dispersing agent is MH4+, Na+ and/or K+. Consequently,
it is preferred to incorporate an advantageous electrolyte,
such as an ammonium or alkali metal base, into an aqueous
slurry to increase deflocculation of the slurry and
thus improve its yield pseudoplasticity.
It is preferred that the dispersing agent(s) used
in the system provide one or more ions to
the system. As used in this specification, the term "ion"
includes an electrically charged atom, an electrically charged
radical, or an electrically charged molecule.
In one preferred embodiment, the dispersing
agent(s) used in the system provides
one or more counterions which are of opposite cha~ge to
that of the surface of the carbonaceous particle3. The charge
on the surface of the carbonaceous particles in water is
generally negative, and thus it is preferred that said
counterions have a positive charge. The most preferred
positively charged ions are the sodium and potassium cations
and the ammonium radical.
In one embodiment it is preferred that the dispersing
agent(~) used in the system be a polyelectrolyte
~2~9~Z6
which, preferably, is organic. As used in this
specification, the term "polyelectrolyte" indicates a poly-
mer which can be changed into a molecule with a number of
electrical charges along its length. It is preferred that
the polyelectrolyte have at least one site on each recurring
structural unit which, when the polyelectrolyte is in
aqueous solution, provides electrical charge; and it is more
preferred that the polyelectrolyte have at least two such
sites per recurring structural unit. In a preferred embodi-
ment, said sites comprise ionizable groups selected fromthe group consisting of ioni~able carboxylate, sulfonate,
sulfate, and phosphate groups. Suitable polyelectrolytes
include, e.g., the alkali metal and ammonium salts of
polycarboxylic acids such as, for instance, polyacrylic
acid; the sodium salt of condensed naphthalene sulfonic
acid; polyacrylamide; and the like.
In one preferred embodiment, the slurry system
contains from about 0.05 to about 4.0 weight percent
by weight of dry solids in the slurry, of an electrolyte
which, preferably, is inorganic. As used in this specifi-
cation, the term "electrolyte" refers to a substance that
dissociates into two or more ions to some extent in water
or other polar solvent. This substance can be, e.g., an
acid, base or salt.
In a more preferred embodiment, the slurry system
is comprised of from about 0.05 to about 2.0
weight percent of an inorganic electrolyte. In the most
preferred embodiment, said system is comprised
of from about 0.1 to about 0.8 weight percent of said
electrolyte. In the most preferred embodiment, the systemcontains from about 0.1 to about 0.5 percent of inorganic
electrolyte.
~ 1y of the inorganic electrolytes known to those
skilled in the art can be used in the system
3~
1~9~L26
Thus1 by way of illustration and not limitation,
one can use the ammonia or alkali metal salt of
hexametaphosphates, pyrophosphates, sulfates, carbonates,
hydroxides, and halides. Alkaline earth metal hydroxides
can be used. Other inorganic electrolytes known to those
skilled in the art also can be used.
In one preferred embodiment, the inorganic
electrolyte is of the formula
Ma~b
wherein M is an alkali metal selected from the group con-
sisting of lithium, sodium, potassium, rubidium, cesium,
and francium; b is the valence of metal M; a is the valence
of anion Z; and Z is an anion selected from the group
consisting of hexametaphosphate, pyrophosphate, silicate,
sulfate, carbonate, hydroxide, and halide anions. It is
preferred that Z be selected from the group consisting o~
carbonate, hydroxide, and silicate anions. The most pre-
ferred electrolytes are selected from the group consisting
of potassium carbonate, sodium hydroxide, and Na2SiO3 9H20.
It is preferred that the slurry system
contain both said dispersing agent(s) and said inorganic
electrolyte(s) and that from about 0.05 to about 10.0 parts
(by weight) of the inorganic electrolyte are present ~or
each part (by weight) of the dispersing agent(s) in the
system.
It is preferred that the total concentration of
both the dispersing agent(s) and/or the inorganic
electrolyte be from 0.05 to 4.0 weight percent.
In one preferred embodiment, the grinding mixt~re
is comprised of dispersing agent(s) and
inorganic electrolyte agent(s) which, when
37
12~91Z~
dissolved in water provide electrically charged ions to
the mixture. The amount of electrically charged ions pre-
ferably present in the mixture ranges from about 0.01 to
about 2.5 weight percent, based upon weight of dry carbonaceous
materials and most preferably i3 from about 0.05 to about 2.0
weight percent. Said concentration of electrically charged ions
can be calculated by first calculating the weights of the
ions in each of the dispersing agent(s) and the electrolyte
agent(s), adding said weight(s), and then dividing the
total ion weight by the weight of the dry coal.
By way of illustration, in one embodiment 0.75
grams of sodium hydroxide and 0.75 grams of sodium decyl ben-
zene sulfonate were added to a mixture comprised of 100 grams
of dry coal. The weight of the sodium ion provided by the
caustic was equal to 22/40 x 0.75 grams; and it equals
0.4125 grams. The weight of the sodium ion provided by the
sodium decyl benzene sul~onate was equal to 22/294 x 0.75
grams; and it equals 0.0561 grams. The total weight of the
sodium ion provided by both the caustic electrolyte and the
sulfonate dispersing agent was 0.4686 grams. Thus, the
slurry contained 0.468 weight percent of sodium ion.
In one embodiment, the grinding mixture is
dilatant. A discussion
of dilatant materials appears at page 5-38 of Perry and
Chilton's ~'Chemical Engineers' Handbook", Fifth Edition
. .
(McGraw-Hill eook Company, New York, 1973), the disclosure
of which is hereby incorporated into this specification
by reference. In general, as is kno~1 to those skilled in
the art, dilatant materials exhibit rheological behavior
opposite to that of pseudoplastics; their apparent viscosity
increases with increasing shear rate.
Some examples of dilatant materials are starch or mica
suspensions in water, quicksand, and beach sand. Extensive
discussions of dilatant suspensions, together with a listing
38
1~Z~9~26
of dilatant 3y3tems, are given by Bauer and Collins
("Thixotropy and Dilatancy" in Eirich, "Rheology", Vol. 4,
Academic, New York, 1967); Green and Griskey, (Trans. Soc.
Rheology 12(1), 13-25, 27-37, 1968); and Griskey and Green
(Am. Inst. Chem. Engrs. J., 17, 725-728, 1971).
It is preferred that the pH of the grinding mixture
be from about 5 to
about 12 and, preferably, from about 7 to about 11. The pH
of the grinding mixture can be adjusted by means well known
to those skilled in the art such as, e.g., by adding alkali metal
hydroxide (such as sodium hydroxide and/or potassium
hydroxide) to the grinding mixture until its pH is within
the target range.
The grinding mixture can be produced
by means well known to those skilled in the art. One such
means will be described below, it being understood that
other comparable means also can be used.
In one process, the grinding mixture
is prepared by a process comprising the steps of (1) preparing
a slurry without fines which slurry contains from about
40 to about 60 weight percent of solid carbonaceous material,
(2) grinding said slurry to a fine Brind
l~ntil the median particle size of the carbonaceous
particles in the slurry is from about 0.5 to about 40
microns; (3) crushing dry coal until at least 98 weight
percent of its particles are smaller than 50 mesh
(300 microns), provided that the median particle size
of the crushed coal exceeds about 40 microns; and (4)
blending the ground slurry and the crushed coal in
specified proportions, together with dispersant.
In the first step of this process, a carbonaceous
A~ _ 3g _
slurry co~prised of from about 40 to about 70 volume
percent of carbonaceous solid material and from about
60 to about 30 volume percent of carrier liquid i3
prepared; it is preferred that the slurry contain from
S about 35 to about 65 volume percent of carbonaceous solid
material and from about 65 to about 35 volume percent of
carrier liquid.
In the second step of this process, the slurry from
step one of the process i~ fine ground in a fine grinder
until the median particle size of its particles
of solid carbonaceous material is from about 0.5 to
about 40 microns and, preferably, from about 1 to about
30 microns. It is most preferred to fine grind the
slurry until the median particle size of its particles of
solid carbonaceous material is from about 2 to about 20
microns. The slurry can be fine ground by means well
known to those skilled in the art. Thus, by way of
example, the slurry can be fine ground in a stirred ball
mill, a colloid mill, a vibratory mill, etc.
In the third step of this process, dry carbonaceous
material i~ separately ground until its median particle
size is greater than about 40 microns and about 98
percent of its particles are smaller than 3/8 inch.
One may start with any size dry coal in thi3 step and grind it.
In the fourth step of this process, the fine and
coarse carbonaceous fractions are mixed until a
grinding mixture with the desired composition is
obtained.
The slurry used in the burning process sf this
invention can be prepared by several different means.
In one of the preferred means, the grinding mixture
is used and is
~.'
i - 40 -
12:~9~26
wet ground until a slurry with specified properties,is
obt~ined. Th~ls, the grinding is continued to produce
a stable, solids-liquid slurry comprising a consist of
finely-divided particles of solid carbonaceous material
dispersed in said liquid, wherein:
(a) said slurry is comprised of at least about 60
volume percent of said solid carbonaceous
material tdrY basis), less than about 40 volume
percent of said liquid, and from
.lO about 0.01 to about 4.0 weight percent (based
on weight of dry solid carbonaceous material) of
dispersing agent;
(b) said slurry has a yield stress of from about 3 to
about 18 Pascals and a Brookfield viscosity at a
solids content of 70 volume percent, ambient
temperature, ambient pressure, and a shear rate
of 100 revolutions per minute of less than 5,000
centipoise;
(c) said consist has a specific surface area of from
about 0.8 to about 4.0 square meters per cubic
centimeter and an interstitial porosity of less
than 20 volume percent;
(d) from about 5 to about 70 volume percent of said
particles of solid carbonaceous material are of
colloidal size, being smaller than about 3 microns;
(e) said consist of finely-divided particles of solid
carbonaceous material has a particle size
distribution substantially in accordance with the
following formula:
.30
41
L91~6
oo ~ ~X~ ( J - Ds~
~-1 L DL;IN~ - V8;~ ,~ J
1~
~here ~ ~ o 1.0
J~l
__ S,~ \
~nd where lf D < D8~ \D N~ _ D N~J
/ DN~ _ DS;~N~ \
and ~h~re lf D ~ DL~ ~ ~ N~ D N~J
wherein:
1. CPFT is the cumulative percent of said solid
carbonaceouq material finer than a certain
specified particle size D, in volume percent;
2. k is the number of component distributions in
the consist and i3 at least 1;
3. X~ i3 the fractional amount of the component
J in the consist, is less than or equal to
1.0, and the sum of all of the X;'s in the
consi~t is 1.0;
4. N i~ the distribution modulus of fraction
and is greater than about 0.001;
5. D is the diameter of any particle in the consist
and range3 from about 0.05 to about 1180
microns;
6. Dq i.~ the diameter of the particle in fraction
~, measured at 1% CPFT on a plot of CPFT versu~
size D, i3 less than DL, and is greater than
0.05 microns;
7. DL is the diameter of the size modulus in frac-
tion ~, mea~ured by ~ieve size or its equiva-
lent, and is from about 10 to about 1180
microns; and
B~ no more than about 0.05 volume percent of the
particles in the slurry consist have a
- 42 -
~9~2~
diameter less than about 0.05 microns;
(f) the net zeta potential of said colloidal size
particles of solid carborlaceous material is from
about 15 to about 85 millivolts; and
(g) the concentration of solid carbonaceous material
in said slurry, the interstitial porosity of said
consist, the specific surface area of said consist,
and the zeta potential of said colloidal size
particles of solid carbonaceous material are inter-
related in accordance with the following formula:
Vs + Ps + SA + 240 = H
wherein:
1. Vs is the percent, by volume, of solid
carbonaceous material in said slurry;
2. P is the porosity of said consist in the
slurry, in percent;
3. S.A. is the specif.ic surface area of said
consist in said slurry, in sq~are meters
per cubic centimeter;
4. Z.P. is the net zeta potential of said
colloidal size particles of carbonaceous
material in said consist, in millivolts, and
5. H is from about 75 to about 98.
The slurry produced by the grinding process
has a yield stress of from about 3 to about 18
Pascals. It i5 preferred that the yield stress be from
about 5 to about 15 Pascals, and it is more preferred that
the yield stress be from about 7 to about 12 Pascals. As
z~
is known to those skilled in the art, the yield stress is
the stress which must be exceeded before flow starts. A
shear stress versus shear rate diagram for a yield
pseudoplastic or a Bingham plastic fluid usually shows a
non-linear hu~p in the rheogram at the onset of flow;
extrapolating the relatively linear portion of the curve
back to the intercept of the shear stress axis gives the
yield stress. See~ for example, W. L. Wilkinson's "Non-
Newtonian Fluids, Fluid Mechanics, Mixing and Heat Transfer"
(Pergamon Press, New York 1960), pages 1-9. Also
see Richard W. Hanks, et al's "Slurry Pipeline Hydraulics
and Design" (Pipeline Systems Incorporated, Crinda,
California, 1980), pages II-l to II-lO, the disclosure
of which is also hereby incorporated herein by reference.
The Brookfield viscosity of the slurry produced by
said process is less than about 5,000
centipoise. The Brookfield viscosity is tested after the
solids concentration of the slurry is adjusted to a solids
content of 70 volume percent (the slurry is either diluted
or concentrated until it has this concentration of solids)
at ambient temperature, ambient pressure, and a shear rate
of lO0 revolutions per minute. It is preferred that the
viscosity of the slurry be less than 4,000 centipoise.
It is more preferred that the viscosity of the slurry be
less than 3,000 centipoise. In an even more preferred
embodiment, the viscosity of the slurry is less than
2,000 centipoise. In the most preferred embodiment, the
viscosity of the slurry is less than 1,000 centipoise.
The term "Brookfield viscosity", as used in this
specification, describes viscosity as meaqured by
conventional techniques by means of a ~rookfield Synchro-
Lectric Viscosimeter (manufactured by the Brookfield
Engineering Laboratories, Stoughton, Mass., U.S.A.).
; - 44 -
~2~91~'6
The solids-liquid slurry produced by the
said process contains a consist of finely-
divided particles of solid carbonaceous material dispersed
in said liquid. Said consist has a
specific surface area of from about 0.8 to about 4.0 square
meters per cubic centimeter. It is preferred that said
specific surface area be from about 0.8 to about 3.0 m2/c.c.
It is more preferred that the specific surface area be from
about 0.8 to about 2.4 m2/cc. In an even more preferred
embodiment, the specific surface area is from about 0.8 to
about 2.0 m2/cc.
As used in this specification, the term "specific surface
area" refers to the summation of the surface area of equivalent
spheres in the particle size distribution as measured by sieve
analysis and sedimentation techniques; the particle size distri-
bution of the consist in the slurry is first determined, it
is assumed that all particles in the COI1SiSt are spherical, and
then one calculates the surface area based on this assump-
tion. As used herein, the term "consist" refers to the
particle size distribution of the solid phase of the
solids-liquid slurry.
For any given consist, one can determine the particle
size distribution by means well known to those skilled in the
art. For measuring particle sizes and for determining
particle size distributions of pulverized and fine grind
carbonaceous particles used for preparing a carbonaceous
slurry, the following two means of measuring particle sizes can
be used and are preferred:
1. U.S. Series sieves Nos. 16, 20, 30, 40, 50, 70, 100,
140, 200, 270, one used to determine weights of
carbonaceous particles passing through each sieve in
the range of about (-) 1180~um to (-) 53 ~m. The
cumulative volume percents of particles, dry basis,
finer than (CPFT) a particular stated sieve size
in microns is charted against the sizes in microns
on a log-log chart, referred to herein as a "CPFT
chart", to indicate the nature of the particle
size distribution of 16 mesh x 270 mesh particles.
2. A Sedigraph*5500L (made by Micromeritics, Co., Nor-
cross, Ga., U.S.) is used to measure particle sizes
and numbers of particles in the carbonaceous material
and in the slurry in the range of (-) 75 ~m to
about 0.2 mm. The Sedigraph 5500L uses photo-extinction
of settling particles dispersed in water according
to Stoke's law as a means for making the above deter-
minations. Cther instruments, such as a Coulter Coun-
ter or combinations of the Leeds ~ Northrup Micro-
trac Particle Analyzers can also be used for similar
accuracy. The results can be plotted on a CPFT chart.
Although these data do not necessarily extend to the
size axi3 at 1% CPFT, the ''Ds at 1%" can be deter-
mined by extrapolating the CPFT chart line to this
axis and reading the intercept. This number,
although not the true Ds, can be effectively u3ed
in the computer algorithm to determine % porosity
and specific surface area.
In addition to the above methods, particle size
measurements can be estimated from methylene blue index
measurement3 to obtain an approximate determination of the
wgt. % of colloidal particles of size below 1 mm. Such a
procedure is described in A.S.T.M. Standard C837-76. This
index can be compared with the surface area calculated
by the CPFT algorithm.
Once the particle size di3tribution of the consist is
determined, it is assumed that each particle in the consist
is spherical with a surface area o ~ ~; the diameter D of
the particles in each clas3 of particles in the consist is
known; and the surface area of the particles in each clas3
* Trademark
- 46
~Z~912~;
is calculated and summed.
The consist in the slurry has an interstitial
porosity of less than about ~0 vo:Lume percent. It is preferred
that said interstitial porosity be less than about
15 volume percent, and it is more preferred that said inter-
stitial porosity be less than about 10 percent. The intersti-
tial porosity is a function of the volume between the inter-
stices of the particles in the slurry consist. For any given
space full of particles, the interstitial porosity is equal to
the "minimum theoretical porosity" in accordance with the
equation presented below.
Minimum Theoretical Porosity = 40% (1 - [1~VA])
where VA is as defined by the following modified Westman-
Hugill algorithm:
VA1 = AlXl
VA2 = Xl + A2X2
VA3 = X1 + X2 + A3X3
.
i--1
VAi = ~, Xj + AiXi
.
n-1
VAn = ~X; + AnXn
J=1
wherein: Ai = Apparent volume of a monodi3persion of the
ith size particle,
Xi = Mass fraction of the ith size particles,
VAi = Apparent volume calculated with reference
~2~12~;
to the ith size particles,
n = Number of particle sizes, and
VA = Maximum value of VAi = Apparent volume of the
mixture of n particle sizes.
To determine the interstitial porosity oY any consist,
the particle size distribution of said consist can be deter-
mined by the method described above with reference to the
measurement of the specific surface area. Thereafter, it
is assumed that each particle in the consist is spherical,
the volume of the particles is calculated in accordance with
this assumption, and the interstitial porosity of the consist
is then calculated in accordance with the above formula. It
is noted that this calculated porosity is less than the true
porosity of a consist as measured, for example, by liquid loss -
due to the non-spherical morphology (shape) of the particles,
and by invocation of Ds at 1%~
The slurry produced by the said process
contains a consist which is comprised of at least about 5
weight percent of colloidal particles, and, preferably,
from about 5 to about 70 weight percent of colloidal
particles. As used herein, the term "colloidal" refers to
a substance of which at least one component is subdivided
physically in such a way that one or more of its dimensions
lies in the range of 100 angstroms and 3 microns. As is known,
these are not fixed limits and, occasionally, systems containing
larger particles are classified as colloids. See Encyclo-
pedia Of Chemistry, 2d Edition, Clark et al tReinhold, 1966),
page 203.
It is preferred that, in said carbonaceous consist,
at least 5 weight percent of
the carbonaceous particles are smaller than about 3.0 microns.
It is preferred that frGm about 5 to about 70 weight percent of
the carbonaceous particles in said consist be smaller than
- 48 -
~12~26
3.0 microns. In one preferred embodiment, from about 5 to
about 30 weight percent of the carbonaceous particles in said
consist are smaller than 3.0 microns. In another preferred
embodiment, from about 7 to about 20 weight percent of the
particles in said consist are smaller than 3.0
microns.
The slurry produced by said process
comprises a compact of finely-divided
carbonaceous particles dispersed in fluid such as,
e.g., finely-divided coal particles dispersed in water.
The term compact, as used in this specification, refers to a
mass of finely-divided partic]es which are closely packed in
accordance with this invention.
The particles in the compact of said slurry
have a specified particle size distribution which
is substantially in accordance with the aforementioned CPFT
formula,
49
1~19~26
wherein CPFT is the cumulative percent of the carbonaceous
solid finer than a certain specif:ied particle size D, in
volume percent; k is the number of component distributions
in the consist, is at least 1, and preferably is from about
1 to about 30, and most preferably is 1; Xj is the fractional
amount of the component j in the consist, is less than or equal
to 1.0, and the sum of all Xj's in the consist is 1.0; n is the
distribution modulus of fraction j, is greater
than about 0.001, preferably is from about 0.001 to about 10.0
and more preferably from 0.01 to about 1.0, and most pre-
ferably is from about 0.01 to about 0.5; D is the diameter
of any particle in the consist and ranges from about 0.05
to about 1180 microns; Ds is the diameter of the smallest
particle in fraction j (as measured by extrapolating the
CPFT chart line, if necessary, to one percent CPFT using
data from sieve analyses plus the Micromeritics Sedigraph
5500L) and is generally greater than 0.05 microns but is
less than DL, and no more than about 0.05 volume percent
of the particles in the slurry consist have a size less
than 0.05 microns; DL represents the diameter of the lar-
gest particle in fraction j (sieve size or its equivalent),
it ranges from about 10 to about 1180 microns, preferably
is from about 30 to about 420 microns, and most preferably
is from about 100 to about 300 microns; DL is the
theoretical size modulus of the particle size distribution;
when CPFT is plotted against size, the DL value is indicated as
the intercept on the upper X axis of the CPFT/D plot.
Hbwever, as is known to those skilled in the art, because
of aberrations in grinding the coarse end of a particle size
distribution, the actual top particle size is always larger
than the DL obtained by, e.g., the particle size equation
described in this case; thus, e.g., a DL size modulus of
250 microns will usually produce a particle distribution
with at least about 98 percent of the particles smaller
~2~ 6
than 300 microns. Consequently, slurry of this invention
has a compact with a particle size distribution which
is substantially in accordance with the CPFT equation;
minor deviations caused by the actual top size being greater
than the DL are within the scope and spirit of this invention.
When k is 1, the aforementioned equation simplifies to:
CPFT Dn _ D n
100 DLn _ D8n
when k is 2, the equation becomes:
(DLlNl -- D~lNI)( DL2N2 - DS2N2)
I II
~21~26
wherein: X1 + X2 = 1.0 (i.e., the sum of the fractional
parts is equal to the whole); when D is less than or equal
to D31, the first term in the parentheses tterm I) is equal
to 0.0; when D is greater than or equal to DL1~ the first
term in the parentheses ~term I) is equal to 1.0; when D
is less than DS2~ the second term in the parentheses (term II)
is equal to 0.0; when D is greater than DL2, the second term
in the parentheses (term II) is equal to 1Ø
The reason for the aforementioned constraints of
the terms in parentheses I and II is that each of these
terms refers to the equation of one of the two components.
In order to sum the fractional parts of the two
component distributions, the above considerations must be
included since particles of a certain size may be repre-
sented between the effective DS and DL of the total distri-
bution but not between the DS or DL of one of the component
distributions. Thus, the values in parentheses I and II are
subject to the limitations that, when D is less than or
equal to Ds, the value for the term is 0.0 and when D is
greater than DLj, the value of the term is 1Ø
The equation given above for when k is 2 is simply
the sum of two components where the fraction of component
i1 is X1 and the fraction of component j2 is X2. Since, in
this case, X1 and X2 make up the whole distribution, their
~um must equal 1Ø
9126
In accordance with the above reasoning, when k - 3,
the equation become3:
CPFT ~ ~1 ( ~ 5l
X2 / D 2 _ DS2
\ DL2N2 - D~2N2 ¦
( DL3N3 _ nS3N3
When k = 4, there is a fourth term in the equation equal to
( DN4 _ DS4~t4
~L2~9~26
In one preferred embodiment, k is 1.
In said slurry, it is preferred that no more than 0.5
weight percent of the solid carbonaceous particles in
the slurry have a particle size less than 0.05 microns.
It i3 preferred that at least 85 weight percent of the
carbonaceous particles in the slurry have a particle size less
than 300 microns. It is more preferred that at least 90
weight percent of the carbonaceous particles in the slurry have
a particle size less than 300 microns. In the most preferred
embodiment, at least 95 weight percent of the carbonaceous
particles in the slurry have a particle size less than 300
microns.
In a preferred embodiment, the fluid is water and the
colloidal sized carbonaceous particles in the slurry have
a net zeta potential of from about 15 to about 85 millivolts.
The following discussion of zeta potential will refer to a
coal-water slurry, it being understood that the discussion
is equally applicable to, e.g., coke-water slurries,
- graphite-water slurries, etc.
It is preferred that the colloidal sized particles of
coal in the coal-water slurry have a net zeta potential
of from about 15 to about 85 millivolts. As used herein,
the term "zeta potential" refers to the net potential, be
it positive ~r negative in charge; thus, a zeta potential
25 of from about 15.4 to 70.2 millivolts includes zeta potentials
of from about -15.4 to about -70.2 millivolts as well
as zeta potentials of from about +15.4 to about +70.2 milli-
volts. In a more preferred embodiment, said zeta potential
is from about 30 to 70 millivolts.
As used in this specification, the term "zeta poten-
tial" has the meaning given it in the field of colloid
chemestry. Concise discussions and descriptions of the zeta
potential and methods for its measurement are found in many
sources including, T.M. Riddick, U.S. 3,454,487, issued July,
9:~6
1969; ~ouglas et al., U.S. 3,976,582 issued August 24, 1976;
Encyclopedia of Chemistry, 2nd edition, Clark et al.,
Reinhold P~bl. Corp. 1966, pages 263-265; Chemical and
Process Technology Encyclopedia, D.M. Corsidine, editor-
in-chief, McGraw-Hill Book Company, N.Y., pages 308-309;
Chemical Technology: An Encyclopedic Treatment, supra,
Vol. VII, pages 27-32; Kirk-Othmer, Encyclopedia of Chemical
Technology, 2nd E~ition, Vol. 22, pages 90-97; and T.M.
Riddick, Control of Colloid_Stability Through Zeta Fotential,
10 Zeta-Meter, Inc. New York City.
"Zeta potential" may be measured by conventional
techniques and apparatus of electroosmosis such as those
described, e.g., in Potter, "Electro Chemistry"; Cleaver-
Hume Press, Ltd.; London (1961). Zeta potential can also
15 be determined by measuring electrophoretic mobility (EPM)
in any of several commercial apparatuses. In the present
invention, a Pen Kem System 3000 (made by Pen Kem Co. Inc.
of Eedford Hills, N.Y.) was used for determining zeta
potential in the examples herein. This instrument is
20 capable of automatically taking samples of coal particles
and producing an EPM distribution by Fast Fourier Transform
Analysis from which the average zeta potential can be
calculated in millivolts.
The zeta potential is measured using very dilute
samples of the < 10 ~m sized coal particles in the coal
compact of the coal-water slurry.
It i3 preferred that the zeta potential of the
colloidal sized coal particles in the coal consist of the
slurry be negative in charge and be from
about -15.4 to about -70.2 millivolts. It is more preferred
that said zeta potential be from about -30 to about -70
millivolts.
- 55 -
12~126
In one embodiment, it is preferred that the zeta
potential of said col]oidally sized coal particles be "near
maximum". "Near maximum zeta potential", as used in this
specification, means a value of zeta potential, measured at
constant electrical conductivity, below the maximum zeta poten-
tial as defined and discussed in the references cited in the
portion of this speci~ication wherein the term "zeta
potential" is defined. It is sometimes necessary to nor-
malize the zeta potential values with respect to the elec-
1 trical conductivity of the carrier fluid because zeta poten-
tial is limited by the electrical conductivity of the carrier
fluid. The near maximum zeta potential should be of a
millivoltage sufficient to provide the coal particles with
a repulsive charge great enough to disperse the coal particles
in the coal-water slurry. In this embodiment, it is
preferred that the zeta potential on the colloidal coal
particles be from about 20 to about 95 percent of the
maximum zeta potential. It is more preferred that the
zeta potential on the colloidal coal particles be from
about 40 to about 80 percent of the maximum zeta potential
for this embodiment.
The maximum zeta potential may be determined by
measuring the Brookfield viscosity of the slurry at different
zeta potentials. For a given system, maximum zeta potential
has been reached when further increases in the surfactant
concentration in the slurry do not further decrease the
Brookfield viscosity of the system at 100 rpm.
Gne preferred means for measuring the zeta potential
is to grind a sample of coal in either a laboratory size
porcelain ball mill with porcelain balls in distilled water
at 30 weight percent solids for approximately 24 hours or in
a steel ball mill with steel balls at 30 weight percent
solids for 16 hours or until all of the particles in the
coal are less than 10 microns in size. ~mall samples
5~
of this larger sample can then be prepared in a known
way by placing them in a vessel equipped with a stirrer with
a sample of water to be used as a carrier in the coal-
water slurry. Various acidic and basic salts are then added
in incremental amounts to vary the pH, and various concen-
trations of various candidate dispersing agent organic
surfactants likewise are added in incremental amounts (e.g.,
grams per grarn coal, both dry basis), alone or in combinations
of two or more. These samples are then evaluated in any
electrophoretic mobility, electroosmosis, or streaming
potential apparatus to determine electrical data, from
which the zeta potential is calculated in a known way.
Plots of zeta potential, pH, and specific conductance vs
concentration may then be made to indicate candidate sur-
factants, or combinations thereof to be used to produce theoptimum dispersion of coal particles in the carrier water
below the amount at which dilatency may be reached.
Several preferred means for producing the slurry used in the
combustion process of this invention are illustrated in Fig. 2.
In a wet grinding method, carbonaceous material is charged to
crusher 10 and crusher 12. In one embodiment, it is preferred that
one carbonaceous material be charged to crusher 10 and
another carbonaceous material be charged to crusher 12.
In another preferred embodiment, different types
of the sarne carbonaceous material are charged to crushers
10 and 12. In this latter embodiment, the carbonaceous
material charged to crushers 10 and 12 can be, e.g.,
coal, a coal fraction which contains less than about
30 weight percent of volatilizable hydrocarbons ~such as,
e.g., anthracite or low volatile bituminous coal) can be
charged to crusher 10, and a coal fraction which
contains more than about 35 weight percent of volatilizable
hydrocarbons (such as, e.g., lignite or high volatile
bituminous coal) can be charged to crusher 12.
~z~
Any of the crushers known to those skilled in the art
to be useful for crushing carbonaceous material can be used as
crusher 10 and/or crusher 12. The same crusher can be used for
crushers 10 or 12, or different crushers can be used. Ihus,
by way of illustration and not limitation, one can use, e.g.,
a rod mill, a ~yratory crusher, a roll crusher, a jaw
crusher, a cage mill, and the like. Generally, the carbonaceous
material is crushed to a size of about 1/4" x 0, although coarser
and finer fractions can be used.
The crushed material from crusher 10 is fed through line
14. The crushed material from crusher 12 is fed through line
16. Part or all of the crushed material from crusher 10 can
be mixed with part or all of the crushed material from crusher
10 by passing the crushed material in line 14 and/or the
crushed material in line 16 through transfer line 18.
Alternatively, transfer line 18 can be closed, the crushed
material from crusher 10 can be fed directly to mill 26, and
the crushed material from crusher 12 can be fed directly to
dry grinder 24.
The crushed material from either crusher 10 or 12 can be
sampled and measured for pH in the ph meter 13, which will be
discussed later, thus establishing a baseline for the entire
control circuit discussed later.
The crushed material from crusher 10 can be fed through
25 line 14 to mill 26. Mill 26 can either be a tumbling
mill (such as a ball mill, pebble mill, rod mill, tube
mill, or compartment mill), or a non-rotary ball or bead
mill, such as stirred mills (including the Sweco dispersion
mill, the Attritor, the Bureau of Mines mill described in
30 U.S. patent 3,075,710), vibratory mills such as the
Vibro-Energy mill, the Podmore-Boulton mill, the Vibratom,
and the like. In generalt the various processes and
apparatuses which can be used to mill the crushed material are
well known to those skilled in the art and are described
58
~Z~.216
in e.g., Perry and Chilton's Chemical Engineer's Handbook,
Fifth Edition (~cGraw Hill, New York, 1973) at pages 8-16
to 8-44 (crushing and grinding equipment).
In one preferred embodiment, mi~l 26 is a ball mill
which, preferably, is run at a reduced speed. In this
embodiment, the mixture is ground at said high solids
content of from about 60 to about 82 volume percent of
carbonaceous material and at a ball mill speed of from about
50 to about 70 percent of the ball mill critical speed.
Thus, for example, the grinding mixture of this invention
can be ground in a ball mill at a speed of from about 50 to
about 70 percent of the ball mill critical speed. The
critical speed of the ball mill is the theoretical speed at which
the centrifugal force on a ball in contact with the mill
shell at the height of its path equals the force on it due
to gravity, and it is defined by the equation
-- ~ 76.6
Nc = D
wherein Nc i3 the critical speed (in rpm), and D is the
diameter of the mill (feet) for a ball diameter that is
small with respect to the mill diameter. It is preferred
to run ball mill 26 at less than about 60 percent of its critical
speed and, more preferably, at less than about 55 percent
of its critical speed. The use of reduced critical speed grinding
produces a 51urry with improved viscosity and stability properties.
In general, mill 26 will have sufficient carbonaceous
material and liquid fed to it so that it will contain from about
60 to about 82 volume percent of carbonaceous material. Crushed
material is fed to mill 2~ through line 14. Alternatively or
additionally, milled carbonaceous material (which might or might
not contain carrier liquid, such as water) from mill 26 can be
recycled through line 40 back into mill 26; this recycled milled
A ~
5 9
~2~ 6
carbonaceous material can be either fine milled material which
passes through a sieve bend 38 and/or coarser milled
material which does not pass through sieve bend 38.
Alternati~ely or additionally, milled carbonaceous material from
mill 46 (which preferably contains carrier liquid) can
be recycled into mill 26 through lines 48, 58, and 60, or into
mill 46 through line 61. Alternatively or additionally,
carbonaceous material ~which preferably contains carrier liquid)
which has been mixed in high shear mixer 64 can be recycled
back into mill 26 through lines 66 and 60, or into mill 46
through lines 61.
Carrier liquid is fed to mill 26 through line 20.
A sufficient amount of said carrier liquid is fed into
the mill 26 so that, in combination with all of the other
feeds to mill 26, a solid-liquid mixture which contains
from about 60 to about 82 volume percent of carbonaceous
material is produced.
~ he mill 26 will have sufficient solids and liquid
fed to it so that it will contain from about 60 to about
82 volume percent of solid carbonaceous material. Generally,
one should charge from about 0 to about 10 volume percent more
solid carbonaceous material to mill 26 than he desires in the
final slurry product, subject to the qualification that in no
event should more than 82 volume percent of such material be
charged to the mill.
Dispersing agent can be added to mill 26 through
line 22. For a given material, dispersant, and solids content,
a given amount of dispersant will optimize zeta potential;
and this amount can be determined in accordance with the
screening tests described in this specification. In general,
a sufficient amount of dispersant is added through line 22
and/or line 62 and/or line 88 so that the slurry
in mill 26 contains from about 0.01 to about 4.0 weight
percent of one or more dispersing agents, based on weight
~2~9~26
of dry carbonaceous material.
A portion of the milled slurry from mill 26 is
passed via line 28 through viscometer 3~9 density meter 32,
ph meter 33, and line 27 back to line 28; a portion of the
slurry passed to density meter 32 is also passed to particle size
distribution analyzer 34. Ihe function of viscometer 30,
density meter 32, ph meter 33, and particle size distribution
analyzer 34 is to continually monitor the quality of the slurry
being produced in mill 26 so that, if necessary, the process
can be adjusted by adjusting the feeds of solids and/or solids-
fluid slurry and/or liquid and/or dispersant and/or ground
carbonaceous material and/or solid-liquid slurry to the mill.
Any of the viscometers known to those skilled in
carbonaceous material and/or solid-liquid slurry to the mill.
the art can be used as viscometer 30. Thus, by way of
illustration, one can use a Nametre Viscometer. The
viscometer 30 indicates the viscosity of the ground slurry.
If the viscosity of the ground slurry is higher than desired,
then either mill 26 is not grinding the coal to produce
a sufficiently high surface area and low porosity, and/or
the amount or type of dispersing agent used is insufficient
to produce a sufficiently high zeta potential on the
colloidal carbonaceous particles; and the underflow slurry
should be subjected to further tests (in density meter 32,
ph meter 33, particle size distribution analyzer 34).
Any of the density meters known to those skilled
in the art can be used as density meter 32. Density
meter 32 indicates the density of the slurry, which
directly varies with its solids content. If the density
of the slurry is lower or higher than desired, then it
is possible that the particle size distribution of the
carbonaceous compact in the underflow slurry is lower or higher
than desired. In this case, the slurry should be
subjected to further tests in particle size analyzer
61
12~9~1Z~
34 to determine what the particle size distribution
of the underflow slurry is and its attendant surface
area and porosity are.
Any ph meters known to those skilled in the art, such
as7 e.g., Leeds ~ Northrup in-line ph meter, can be used as
ph meter 33. The ph meter measures the hydrogen ion
concentration of the slurry, which can vary with water quality,
the oxidation state of the carbonaceous or pyrite surfaces,
soluble ingredients within the carbonaceous material, or errors
in dispersant additions~
Particle si~e distribution analyzer 34 analyzes
the particle size distribution of the compact of the
underflow slurry. Any of the particle size distribution
analyzers known to those skilled in the art, such as, e.g.,
Micromeritics Sedigraph 5500L, Coulter Counter, ~eeds and
Northrup Microtrac Particle Analyzers, can be used as
analyzer 34. From the data ~enerated by analyzer 34, the
specific surface area and the porosity of the compact of
underflow slurry can be determined.
Ground slurry from mill 26 is passed through line 28
to sieve bend 38. Sieve bend 38 may be 40 mesh sieve which,
preferably, allows underflow slurry of sufficient
fineness tsuch as, e.g., less than 420 microns) through
to line 29 into mill 46 where it is subjected to further
grinding; alternatively, all or part of this fine ground
slurry can be recycled into mill 26 via line 40. Cverflow
particles which are greater than 420 microns are recycled
via line 40 back into mill 26, where they are subjected
to further grinding.
The ground slurry from mill 26 which passes through
sieve bend 38 can be passed through line 29 to mill 46.
Mill 46 can be a rod mill, a ball mill, or a stirred
ball mill; it preferably is a ball mill. It is preferred
that the slurry be passed to mill 46 until at least about 95
62
~9:3 2~
volume percent of the particles in the slurry have particles
less than about 20 microns, and, more preferably~ less than
about 15 microns; in the most preferred embodiment, the
slurry in mill 46 is ground until at least 95 volume percent
of the particles in the slurry have diameters less than
about 5 microns. Additional liquid and/or dispersant can be
added to mill 46 via line 59 if necessary.
A portion of the ground slurry from mill 46 is passed
through a control circuit comprised of viscometer 50,
density meter 52, and particle size distribution analyzer 54,
pH meter 53, and line 56,
wherein the slurry is analyzed as described above for the
slurry passing from line 28 into viscometer 30, density
meter 32, ph meter 33, and particle size distribution analyzer 34.
The feed to mill 46 can be adjusted, as required, by feeding
crushed carbonaceous material from a dry grinding mill 24
and/or by adjusting the feeds to mill 26.
Sl~rry from density meter 52 is returned through
line 56 to line 48. Part or all of ground slurry from
mill 46 can be passed through lines 48, 58, and 60 back
to mill 26, wherein it i~ fed as a recycle stream.
Alternatively, or additionally, part or all of ground
slurry from mill 46 can be passed via line 61 to mill 46
as a recycle stream. Alternatively, or additionally,
part or all of ground slurry from mill 46 can be passed
into high shear mixer 64. Any of the high shear, high
intensity mixers known to those skilled in the art can be
used as high shear mixer 64 and/or high shear mixer 86. Thus,
by way of illustration and not limitation, one can use for the
high shear mixer(s) a Banbury mixer, a Prodex-Henschel mixer,
a Welex-Papenmeir mixer, and the like. These high-shear,
intensive mixers are described on page 19-17 of Perry and
Chilton's Chemical Engineer's Handbook, (McGraw Hill, New
York, 1973).
- 63 -
.2~i
Dispersing agent i3 passed through line 62 to high
shear mixer 64 to optimize the zeta potential of the
colloidal particles of the slurry in the mixer. A
sufficient amount of dispersing agent is charged to this
mixer so that the final coal slurry product contains
from about 0.01 to about l~.o weight percent of dispersant,
based on the weight o dry coal.
Some or all of the product from high shear mixer
64 can be recycled via lines 66 and 60 to ball mill 26, or via
line 61 to mill 46. Alternatively or additionally, some or all
of the product from high shear mixer 64 can be fed through line
68 to hopper 70 and thence to Moyno pump 74 for volumetric blending.
The "Moyno pump", also referred to as a "progressive
cavity" or "moving cavity" pump, is well known to those
skilled in the art. It consists of a convoluted hardened
steel rotor and an inverse convoluted elastomeric stator so
designed that as the rotor turns it maintains full contact
with the stator on one side and only point to point contact
with the stator on the other side. This produces a sealed
cavity which moves in the direction of di3charge as the
rotor turns. ~sing a variable speed drive this pump can
deliver variable volume flow rates at reasonable pressures
and at high viscosities. Using a pair-of pumps as 74 and
75 allows accurate blending volumetrically of two converging
streams of fluids. This is described on pages 19-14 to 19-23
of Perry ~ Chilton's Chemical Engineers Handbook, 5th edition,
supra.
The function of the Moyno pump in the process is to
deliver the proper volumetric proportions of two streams
from lines 68 and 42 or hoppers 70 and 72 to line 73 to
low shear blender 76 via line 73. The blend from blender 76
is then transferred via line 77 using Moyno pump 78 through
line 80 to a cleaning apparatus 82.
- 64 -
3LZ3L~ 2 6
Material from Mbyno pump 74 can be fed through line 73
to low shear blender 76. Any of the low shear blenders
known to those skilled in the art can be used. Thus, by
way of illustration and not limitation, one can use a
twin-blade conical mixer (Atlantic Research Corp.), a
double-arm kneader mixer (Baker Perkins Inc.), a helical
ribbon mixer, gate mixers, Poly-Eon continuous reactors
(~aker Perkins), the Rietz Extructor, Ko-Kneader (Baker
Perkins), Transfer mix (Sterling Extruder Corp.), Rotofeed
(Baker Perkins), ZSK (Werner-Pfleiderer), Halo-flite
Processor (Joy Mfg. Co.), Kneadermaster (Patterson Industries
Inc.), etc. Thereafter, the product from low shear blender 76 can be
fed through line 77 to Moyno pump 78 and thence through
line 80 to cleaner 82.
Cleaned slurry from cleaner 82 can be passed through
line 83 to high shear mixer 86. Alternatively, or
additionally, cleaner 82 can be bypassed in whole or in
part and product from Moyno pump 78 and/or mill 24 can be
passed through lines 17 and 84 to high shear mixer 86. Required
amounts of dispersant and liquid are fed in lines 8~ and
90, respectively to the high shear mlxer. A final control
circuit, comprised of viscometer 94, density meter 96, line 92,
particle size distribution analyzer 98, zeta meter 100,
ash and sulfur analyzer 102 and ph meter 103, allows one to
analyze a portion of the slurry being produced in high shear
mixer 86 so that appropriate adjustments can be made in the
feeds.
Any of the zeta meters known to those skilled in the
art can be used as zeta meter 100. Similarly, any of the
ash and sulfur analyzers known to those skilled in the art
can be used as analyzer 102.
Figure 2 also illustrates a dry grinding process for
making the slurry of this invention. In this process,
which may be used separately andtor in conjunction with
~2~9~Z~
the wet grinding process, crushed solid carbonaceous
material from crusher 12 is passed through line 16 to dry
grinder 24; part or all of the material from crusher 12
may alternatively be passed through transfer line 18 to
be mixed with solid carbonaceous material from crusher 10 and
thence passed through line 14 to mill 26. Any of the dry
grinders known to those skilled in the art can be used as grinder
24. Thus, by way of illustration and not limitation, one
can use a hammer mill. Ihus, e.g., one can also use ball
mills or the ring roller mills described on pages 8-33
and 8-34 of Perry and Chilton's Chemical Engineer's Handbook,
5th edition, supra. It is preferred to ground the crushed
material in dry grinder 24 until it is pulverized, that
is until it is a consist of about 40 mesh by 0.
The pulverized solid carbonaceous material fro~ dry grinder
24 can be passed through line 44 to mill 46 wherein it may be
mixed with the feed from line 29 (or, alternatively, not mixed
with any such additional feed) and thereafter processed as
described hereinabove. Alternatively, or additionally,
part or all of the pulverized material from dry grinder 24
can be passed through line 15 and line 14 to mill 26.
Alternatively or additionally, part or all of the pulverized
carbonaceous material from dry grinder 24 can be passed through
line 17 and fed directly into high shear mixer 86, where it is
blended with liquid and dispersant and ground to make carbonaceous
material-liquid slurry.
In another embodiment, illustrated in Fig. 2, part or
all of the underflow slurry which passes through sieve
38 can be passed through line 42 to hopper 72 and thence
to Mbyno pump 75. The product from Moyno pump 75 is then
passed through line 73 to low shear blender 76 and processed
as described above.
The operation of the control circuit comprised of
viscometer 94, density meter 96, particle size distribution
2~;
analyzer 98, zeta meter 100, and ash and sulfur analyzer 102
will now be described, it being understood that the other
control circuits in the proces3 operate in a similar
manner.
ln Fig. 2, control ciruits are showl~ which are comprised
of a viscometer, a densitometer, a particle size analyzer,
and a pH meter. As will be apparent to those skilled in the
art, fewer or more such control circuits can be used in
the process, and the control circuits can be located at
points in the process other than those indicated in Fig. 2.
A typical control circuit is comprised of viscometer
30, densitometer 32, particle size analyzer 34, and pH
meter 33. l~is circuit contil1ually monitors the viscoslty,
density, consist particle size distribution, and pH of
the slurry, and it adjusts the process so that these
factors are properly interrelated.
If the density of the slurry is not within the target
range, or if the viscosity is too low, then the control
circuit determines this and adiusts the ratio of the solids
flow rate in the process to the liquids flow rate in the
process, thereby adjusting the solids/liquids ratio.
If the viscosity of the slurry i3 higher than the
target ral1ge, then the control circuit determines this
and adjusts the dispersant concentration (insufficient
dispersant can cause a viscosity increase), the solid
and/or the liquid flow rate (an insufficient liquid flow
rate will cause the solids/liquids ratio to be too high,
and will thus cause the viscosity to increase), the pH
(if the pH of the grinding mixture is too low, the
viscosity might be too high), and/or the particle size
distribution. The pH of the grinding mixture can be
adjusted by adding more dispersant and/or caustic. It is
to be understood that all of these factors are interrelated,
and that the control circuit can, and preferably does,
~9~2~
monitor and adjust all of these factors simultaneously.
For any given solids-slurry system, the target
particle size distribution can be determined by analyzing
"ideal" slurry and determining its particle size
distribution; an "ideal" slurry is one which has the
required solids content and viscosity and which fits
into the equations described else~here in this specification.
The particle size distribution of this "ideal slurry" can
be determined 0l1 two Leeds and Northrup Microtrac Particle
Analyzers-the Extended Range Analyzer (300 - 3,um) and the
Small Particle Analyzer (21 - 0.1 ~m). lhe percent of the
particles in the slurry consist which are less than 300
microns, 212 microns, 150 microns, 106 microns, 75 microns,
53 microns, 38 microns, 27 microns, etc. can be determined.
Then, armed with this particle size profile for the ideal
slurry, the particle size analyzer in the control circuit
can continually analyze the particle size distribution of the
slurry in the process and, if it is less than ideal, the
control circuit can adjust the process accordingly. In
general, the percent of the particles in the slurry consist
which are less than a certain specified particle size can be
adjusted by adjusting the relative feed rates of the solids
and the liquids fed to the system. For example, if the
particle size analyzer indicates that the percent of the
particles in the consist less than 212 microns is not
within the target range, this can be adjusted by varying
the dry carbonaceous material feed rate. For another example,
a change in the entire particle size distribution of the slurry
consist, including the percent less than 212 um, can be made by
varying the solids/liquids ratio, i.e., by adjusting the
volume percent solids in the grinding mixture.
Of particular importance in the particle size
distribution analysis is the control of the "n" and the
specific sur~ace area of the slurry consist. The "n"
68
~9iL26
in the particle size distribution equation is proportional
to the difference between the weight percent concentrations
of two selected channels in the Microtrac ER analyzer; the
difference between the weight percent concentrations of,
e.g., particles less than 150 microns and particles less
than 53 microns can be determined for the aforementioned
"ideal" slurry; and, armed with this "ideal difference"
between said concentrations, the particle size analyzer
can continually determine this difference for the slurry
in the process and, if it varies from the ideal, the control
circuit can adjust the relative feed rates of the solids
and liquids fed to the system. The specific surface area
of the consist in the slurry is proportional to the
difference between the weight percent concentrations of
two selected channels in the Microtrac SP~ analyzer;
the difference between the weight percent of, e.g.,
partîcles less than 1.01 and 0.34 microns can be
determined for the aforementioned "ideal slurry"; and,
armed with this "ideal difference", the particle size
analyzer can continually determine this difference for
the slurry in the process and, if it varies from the
ideal, the control circuit can adjust the relative feed
rates of the solids and liquids fed to the system.
The control system described in FiB. 2 is capable,
thus, of continually monitoring and adjusting the slurry
solids content, the slurry viscosity, the particle size
distribution of the slurry consist, the "n" of the slurry
consist, and the specific surface area of the slurry
consist.
As indicated above, if the viscosity of the slurry
is higher than the target rate, the control circuit
determines this and can adjust the dispersant concentration
and/or the solid flow rate and/or the liquid flow
rate and/or the pH. Alternatively, or additionally, the
69
control circuit can adjust the amount of reground
carbonaceous fine material being recycled to the grinding
mill; an insufficient amount of colloidally sized
carbonaceous material in the slurry consiat will cause the
viscosity of the slurry to be too high, and the addition
of finely ground carbonaceous material to such a slurry
tends to reduce its viscosity. For example, if viscometer
30 determines that the slurry in mill 26 is too viscous,
lt can cause finely ground carbonaceous material from
mill 46 and/or high shear mixer 64 to be recycled through
line 60 to mill 26, thereby increasing the amount of fine
material in the grindin~ mixture in mill 26 and tending to
lower its viscosity. For example, if viscometer 94 determines
that the slurry in high shear mixer 86 is too viscous, it
can cause finely ground carbonaceous material from mill 46
and/or high shear mixer 64 to be recycled through line
60 to mill 26, thereby increasing the amount of fine
material in the slurry ultimately fed to high shear mixer
86 through line 84; it can recycle finely ground
carbonaceous material from mill 46 through lines 48, 58,
60, and 61 back into mill 46; it can recycle finely
ground carbonaceous material from high shear mixer 64 through
lines 66, 58 and 48 back into high shear mixer 64; it can
recycle finely ground carbonaceous material from mill 26
through lines 28 and 40 back into mill 26; it can do any
combination of the aforementioned steps; and the like.
The aforementioned means of increasing the amount of finely
ground carbonaceous material in mills 26 and 46 and mixers
64 and 86 are only illustrative, and those skilled in the
art upon an examination of Fig. 2 will appreciate other means
which can be used.
Thus, the control circuit can adjust the viscosity of
the slurry in mill 26 by adjusting the amount of carbonaceous
material fed through line 14, the amount of carbonaceous
~2~
material fed through lines 16 and 18, the amount of
carbonaceous material fed through line 15, the amount of
carrier liquid fed through line 20, the amount of
dispersant fed through line 22, the amount of finely
ground carbonaceous material recycled through lines
28 and 40, the amount of finely ground carbonaceous
material recycled through lines 48, 58, and 60, the
amount of finely ground carbonaceous material recycled
through lines 66 and 60, and/or the pH. Thus, the control
circ~it can adjust the viscosity of the slurry in mill
through lines 66 and 60, and/or the pH. Thus, the control
of the grinding mixture in mill 46 can be done by adjusting any
or all of the aforementioned factors influencing the slurry
viscosity in mill 26, (for the properties of the slurry coming
out of mill 26 influence the properties of the slurry formed in mill
46), and, additionally or alternatively, the amount of
carbonaceous material fed to mill 46 through line 44, and the
amount of carbonaceou~ material fed to mill 46 through line 29
Thus, the control circuit can adjust the viscosity of the slurry
in high shear mixer 64 by adjusting any or all of the aforemen-
tioned factors influencing the slurry viscosity in mills 26 and
46 (for when the properties of these slurries are changed,
they change the properties of the slurry in mixer 64) and,
alternatively or additionally, the amount of dispersing
agent added through line 62, and the amount of finely
ground carbonaceous material recycled through lines
66 and 58 to mixer 64. Thus, the control circuit can
adjust the viscosity of the slurry in high shear mixer
86 by adjusting any of the aforementioned factors
influencing the slurry viscosity in mill 26, mill 46,
and high shear mixer 64, and, alternatively or
additionally, the amount of dispersing agent fed to mixer
86 through line 88, the amount of carrier liquid fed to
mixer 86 through line 90, the amount of dry carbonaceous
~9~2~;
material fed to high shear mixer through line 17, the
amount of finely ground carbonaceous material fed through
line 42 to hopper 72, the pH of the slurry in mixer 86,
and the like.
Cleaner 82, referred to in Fig. 2, can be any of the
carbonaceous-slurry cleaning apparatuses known to those
skilled in the art. Thus, by way of illustration and not
limitation, one can use the electrophoretic deashing
cell illustrated on page 3 (Fig. 3) of Miller and
Baker's Bureau of Mines Report of Investigations 7960
(United States ~epartment of the Interior, Bureau of
Mines, 1974), the disclosure of which is hereby
incorporated by reference into this specification.
Thus, one can clean said slurry by passing it onto a
sedimentation device, such as a lamella filter, where it
is allowed to settle. Thus, one can effect magnetic
separation of the slurry and/or combine such magnetic
separation with sedimentation in the form of a pre- or
post-treatment step.
In one preferred embodiment, cleaner 82 involves the
cleaning process described in U.S. patents 4,186,887, and 4,
173, 530, the disclosures of which patents are hereby incorporated
by reference into this application. In this preferred embodiment,
it is preferred that no dispersing agent be added to the carbonaceous
material-fluid mixture until after the mixture has passed through
cleaner 82 into high shear mixer 86, at which time the
required amount of dispersant is added; thus, in this
preferred embodiment, no dispersing agent is added to mill
26.
In one preferred embodiment, the carbonaceous solid
material in the grinding mixture (and in the slurry
produced therefrom) contains less than about 5 weight
percent of ash. The term "ash", as used in this
specification, includes non-carbonaceous impurities such
72
~21~2~
as, e.g., inorganic sulfur, various metal sulfides, and
other metal impurities as well as soil and clay particles.
The fraction of ash in the carbonaceous material can be
calculated by dividing the weight of all of the non-
carbonaceous material in the slurry solids by the totalweight of the slurry solids (which includes both
carbonaceous and non-carbonaceous material).
It is preferred that the slurry have a pH from about 5 to
about 12 and, preferably, from about 7 to about 11.
Conventional means may be used to adjust the pH of the
slurry so that it is within these ranges.
In one preferred embodiment, the slurry possesses a unique
property; its viscosity decreases at a constant shear
rate with kime, at an increasing shear rate, and at an
increasing temperature; this property greatly enhances
the pumpability o~ the slurry.
In one embodiment, the slurry is a yield-pseudoplastic fluid.
The term "yield pseudoplastic fluid"~ as used in this
specification, has the usual meaning associated with it
in the field of fluid flow. Specifically, a yield
pseudoplastic fluid is one which requires that a yield
stress be exceeded before flow commences, and one whose
apparent viscosity decreases with increasing rate of shear.
In a shear stress vs. shear rate diagram, the curve for a
yield pseudoplastic fluid shows a non-linearly increasing
shear stress with a linearly increasing rate of shear. In
a "pure" pseudoplastic system, no yield stress is observed
so that the curve passes through the origin. However, most
real systems do exhibit a yield stress, indicating some
3 plasticity. For a yield pseudoplastic fluid, the viscosity
decreases ~ith increased shear rate.
In an even more preferred embodiment, the slurry
produced by the process is also thixotropic, i.e., its
viscosity decreases with time at a constant shear rate,
:12~2~
Furthermore, in this embodiment, the slurry has a
negative temperat~re coefficient of viscosity, i.e., its
viscosity decreases with increasing temperature.
In the process of this invention, the carbonaceous
slurry is atomized prior to the time it is burned.
Atomization is a process of breaking a liquid into a multitude
of tiny droplets. In a preferred embodiment, the slurry is
heated before atomization to effectively vaporize the carrier
liquid in the slurry. Heating may not be necessary since the
atomization of the slurry exposes the interstitial water
to the high temperature flame which causes vaporization at
that time.
Any of the atomizing apparatuses known to those
skilled in the art can be used in the process of this
invention. Thus, by way of illustration and not limitation,
one can use spray nozzle atomizers to atomize the slurry.
The preferred spray nozzles are selected from the group
consisting of pressure nozzles, two-fluid devices, and rotary
nozzles. Thus, e.g., one can use sonic energy ~from gas streams~,
ultrasonic energy (electronic), and electrostatic energy to
atomize the slurry. Some of the nozzles which can be used in
the process of this invention are described in Tate,
"Chemical Engineering", July 19, 1965, page 157 and Tate,
"Chemical Engineering", August 2, 1965, page 111.
Some of the preferred atomizing nozzles are described
on pages 18-61 through 18-63 of Perry and Chilton's "Chemical
Engineers' Handbook", Fifth dition, (~cGraw Hill Book Co.,
New York, 1973). The disclosure of page 18-61 to 18-63 of
this reference is hereby incorporated by reference into this
specification.
Hbllow cone spray nozzles can be used in the process
~'
~IJ - 74 -
~9126
of this invention to atomize the slurry. In these types
of nozzles, the liquid leaves as a conical sheet as a result
of centrifugal motion of the liquid, and the air core extends
into the nozzle. Thus, e.g., one can use the Whirl-chamber
hollow cone, where a centrifugal motion is developed by
tangential inlet in the chamber upstream of the orifice. Thus,
e.g., one can use a grooved core, where centrifugal motion is
developed by inserts in the chamber.
Solid cone spray nozzles can be used in the process
of this invention to atomize the slurry. These nozzles, which
are similar to the hollow cone spray nozzles, differ from them
in that they contain an insert to provide even distribution.
Fan (f`lat) spray nozzles can be used in the process
of this invention to atomize the slurry. In these nozzles,
the liquid leaves as a flat sheet or a flattened elipse.
Thus, e.g., one can use the Cval-orifice fan nozzle (or a
rectangular orifice nozzle) wherein the combination of the
cavity and the orifice produces two streams that impinge
within the nozzle. Thus, e.g., one can use the Deflector jet
nozzle wherein liquid from a plain circular orifice impinges
upon a curved deflector. Thus, e.g., one can use Impinging jet
nozzles, where two jets collide outside of the nozzle and
produce a sheet perpendicular to their plane.
Spray nozzles with a relatively wide range of turn down
can be used in the process of this invention to atomize the
slurry. Thus, e.g., one can use Spill (by-pass) nozzles wherein
a portion of the liquid is recirculated after going through the
swirl chamber. Thus, e.g., one can use Poppet nozzles, wherein
a conical sheet is developed by flow between the orifice and the
poppet, and increased pressure causes the poppet to move out and
- increase the flow area. Thus, e.g., one can use ~ual-orifice
nozzles, wherein two concentric orifices, each with its o~
liquid supply system, are used; in these nozzles, the conical
sheets impinge so that the high-velocity stream provides
~9~2t~
atomization energy.
Two-fluid atomizers can be used in the proces~ of this
invention to atomize the slurry. In these atomizers, gas
impinges upon the "coaxial" (inner flow of liquid) and supplies
energy for break up.
Rotary atomizers can be used in the process of this
invention to atomize the slurry. In these nozzles, liquid
is fed to a rotating surface and spreads in a uniform film.
Thus, e.g., flat disks, disks with vane3, and bowl-shaped
cups. In most of these nozzles, liquid is thrown out at
90 degrees to the axis.
Since coal particles traveling at velocities sufficient
for effective atomization can cause severe erosion, or wear,
on metal parts, it is preferred that these parts be made from
abrasion resistant materials such as A1203,SiC, WC ceramics,
or the like.
Fig. 3 is a cross-sectional view of a typical atomizer
or turbulent flow, burner in which the slurry described in this
specification can be burned. Atomizing burner 150 of furnace 151
20 is comprised of central nozzle 152, guide vanes 154, ring of air
control vanes 156, and firewall 160. Carbonaceous slurry is
injected into the apparatus at point 162, into central nozzle
152. Air is injected into the apparatus at points 164 and/or
1~6.
It is preferred that the slurry which is fed into the
atomizing burner 150 have a Brookfield viscosity, when
measured at a solids content of 75 weight percent, ambient
temperature and pressure, and 100 revolutions per minute, of
less than about 2000 centipoise. It is even more preferred
that the slurry have a Brookfield viscosity under said test
conditions of less than about 1500 centipoise. It is even
more preferred that said slurry have a Brookfield viscosity
under test conditions of less than about 1000 centipoise.
The use of a low-viscosity slurry improves atomization quality
and allows one to obtain stable ignition. It is desired that
the viscosity of the slurry under the conditions of atomization
be minimal. In the case, e.g., of a Newtonian fluid, a low
Brookfield viscosity generally corresponds to a low atomization
vi~cosity.
The slurry ~sed in the burning process of this invention
has a negative temperature coefficient of viscosity; its
viscosity decreases with increasing temperature. Thus, in
one preferred embodiment, it is preferred to heat the slurry
to a temperature exceeding about 215 degrees Fahrenheit prior
to the time the slurry is injected into the atomizing
burner 150.
The carbonaceous slurry described in this specification
can be burned directly in conventional liquid-fluel handling
equipment. Fig. 4 illustrates a conventional, commercial
oil burner to which minor modifications have been made to
optimize burner performance and combustion efficiency;
this burner is described in a publication by T.M. Sommer and
J.E. Funk entitled "Development of a High-Solid, Coal-Water
Mixture for Application as a Boiler Fuel" which was
contributed by the Fuels Dlvision of the American Society of
Mechanical Ehgineers for presentation at the joint ASME/IEEE
Pbwer Generation Conference, Cctober 4-8, 1981, St. Louis,
Missouri (pages 1-4); the disclosure of this publication
is hereby incorporated by reference into this specification.
Referring to Fig. 4, burner 200 is comprised of natural
gas igniter 202, atomizer 204, air control register 206,
natural Kas burner 208, and swirler-impeller 210.
The followlng example is presented to illustrate
certain aspects of the invention but is not to be deemed
limitative thereof. Unless otherwise specified, all parts
are by weight and all temperatures are in degrees centigrade.
Example 1 - Preparation of Coal Samples for Measuremeots
r
~ .
~ - 77 -
Z6
(a) Sieve analysis
Although any standard procedure may be used to
measure particle sizes of coal particles from a coal and
then to calculate the particle size distribution, the
procedure used in obtaining data discussed herein will be
described.
A weighed sample, e~g. 50 grams dry wgt. of coal
is dispersed in 400 m.l. of carrier water containing 1.0
wgt. % Lomar D based on a weight of coal, dry basis, and
the slurry is mixed for 10 minutes with a Hamilton Beach
mixer.
The sa~ple is then remixed very briefly. It then is
poured slowly on a stack of tared U.S. Standard sieves
over a large vessel. The sample is carefully washed
with running water through the top sieve with the rest
of the stack intact until all sievable material on that
sieve is washed through the sieve into the underlying
sieves. The top sieve is then removed and each sieve
in the stack, as it becomes the top sieve, is successively
washed and removed until each sieve has been washed. The
sieves are then dried in a dryer at 105C and the residue
on each is weighed in a known way.
(b) Sedigraph analysis
A separate sample finer than 140 mesh sieve size
is carefully stirred and a representative sample (about
200 m.l.) is taken for analysis. The rest may be discarded.
About 2 eyedroppers of the dilute slurry are further
diluted in 30 m.l. of distilled water with 4 drops of Lomar D
added. This sample is stirred overnight with a magnetic
stirrer. Measurement is then made with the ~edigraph 5500L.
The Sedigraph 5500L uses photo extinction to measure
particles. It essentially measures projected area of
shadows, and the data must be converted to volume-%-finer-
than. The data from the sieve and Sedigraph is combined
78
1~9~
to prepare a CPFT chart. Ds at 1% is read from the CPFT
line.
It is to be understood that the foregoing description
and Example are illustrative only and that changes can be
made in the ingredients and their proportions and in the
sequence and combination of process steps as well as other
aspects of the invention discussed without departing from
the scope and spirit of the invention as defined in the
following claims.
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