Note: Descriptions are shown in the official language in which they were submitted.
SLURRY ()1~` ~`OAL-WI~T~.R-I~N:LONIC ORG/~NIC
SURF~CTAN'r
U~C~GROU~I) 0~ T~IE INVENI'ION
Tllis inverltion r~lates to a me~:hod for preparing
and utilizin~ a partially de-~she(l coal-wa~r slurry for
generation of heat energy in a furn~ce provicle~ witI~ slurry
conveying means and a coal-slurry atomizer-burner.
More particularly, this i.nvention relates to
an improved partially de-ashed coal-water slurry having
pseudoplastic rheological properties.
Processes for preparing aIld ut~ ,ing p~ Lly
de-ashed solid-luel-water slurries and conveyin~ the sLu~ry
by various conveying means, such as pumps, are known. O. Schwartz
and H. Merten, ~rennstoff l~aerme Kraft 18 (10), 474-~ (1966)
(Ger) describe a pilot plant in which coal t~as pulverized
- dry or wet in ball mills an~ disk grinders t.o provide parti.cles
up to 77% -iner than 0.06 mm.
'
~..,'~''
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Coal-water slurries containing :Erom 40 to 60% by weight
of coal were so prepared. Piston, centrifugal and screw
pumps were used to pump the slurry. Settling was avoided
by using flow rates in the turbulent range. A rotation
atomizer was found better tl~an a pressure atomizer for
burning the slurry.
U.K. Patent #711,105 teaches wetting pulverized
coal particles with aromatic or aliphatic oil wetting agents,
to cause separation of clay and other waste particles from
` the oil-wetted coal particles in a water flotation process
using impact plate mills to obtain the necessary
dispersion of the particles. The pH of the pulp of coal
and debris particles is taught to be carefully maintained -
to obtain economic recovery of the coal particles. The
operation can be carried out underground and the pulp or
recovered coal-water slurry pumped to an above-ground
station for separation of the water from the coal particles.
French Patent ~1,581,112 teaches preparing and
- burning aqueous slurries containing about 60 wgt% coal
by mixing coal dust filtered from washing water already
- containing ultrafine coal par~icles, to prevent buildup
of suspended and dissolved material.
U.S. 3,423,313 teaches separation of a high
solids content underflow from the liquid phase of a low-
solids con~ent slurry in a mechanic21-type thickener
utilizing flocculant materials. The thickeners may be
used for water clarification in the coal mining industry
and for recovering coal fines.
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U.S. 3,996,026 teaches preparation of a finely-
divided solid fuel-water mixture having a total water content
between 35 and 55% by weight and containing sufficient
organic liquid of a type selected to improve pumpability
of the slurry, such as, naphtha. The slurry is then
heated to maintain the water under pressure and in the
liquid phase. The organic liquid is removed rom the
slurry prior to injecting the remaining mixture into a
solid fuel gasification zone. The process relates to
the gasification of coal to provide gaseous fuel or
synthesis gas.
U.S. 3,682,114 teaches a method for atomizing a
coal liquid suspension consisting of pulverized coal
- and water in approximately 60 to 40 weight ratio. Other
liquids, such as methanol, which are low-boiling also are
taught to be used in the slurry. The coal is maintained
in suspension by mechanical means such as an agitator,
prior to being pumped to an atomizer attached to the
furnace of a steam boiler~
U.S. 3j950,147 teaches a process for converting
coal or the like particles into gas, heat, or gas and
heat~ within a pressurized processing chamber in which
particles of the coal are maintained during processing
in an agitated cond~ion and wherein the coal is finely
pulverized and separated from larger particles, and
e~entually rom the liquid, and fed in dry form to the
processing chamber.
~ P4~7 ~ ~
U. S. 3,9~1,552 teaches a process wherein pulverized
coal is slurried with water then with oil, or if desired, oil
and pulverized alkalies. Preferably lime or limestone is added,
and the mixture is subjected to sonic vibrations to produce a
li~uid suspension of the coal. Lime is used optionally to reduce
the sulfur dioxide in burning where the coal contains sulfur.
The resulting dispersion is utilized and burned in a furnace.
The above processes all relate to coal-water slurries
in which mechanical agitation or sonic vibration are used or
- 10 oil, or other liquid, is added to the slurry to maintain the
coal particles in suspension in the water phase prior to feeding
- it to a burner or gasifier unit. In contrast to these prior
art processes, the process of the present invention utilizes an
-~ anionic organic surfactant as a deflocculating agent to convert
a high solids coal-water slurry to a pseudoplastic mass which
can be pumped in a pipeline.
~.
DESCRIPTION OF THE DRAWING
The features and benefits of ihe present invention
will become more apparent from the following description with
reference being made to the accompanying drawing, the preferred
embodiments, and the specific Example. In the drawing, Figs. 1
and 2 are shear diagrams. Figs. 3, 4 and 5 are deflocculation
curves of pseudoplastic coal-water-anionic organic surfactant
slurries made according to the invention. Fig. 6 is a flow
diagram for an integrated process for preparing and utilizing
a pseudoplastic coal-water-anionic organic surfactant slurry
to generate heat. Fig. 7 is a cross-section of a typical
atomizer for combustion of the coal-water-anionic organic
surfactant slurry of this invention.
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SUMMARY OF THE INVENTION
. _
The present i~vention relates to a novel deflocculated
coal-water slurry which has pseudoplastic properties to enhance
pumpability of the slurry. In the slurry, pulverized coal is
maintained in deflocculated condition in the water. The slurry
is deflocculated and simultaneously rendered pseudoplastic by
the presence in the slurry of an effective amount of an anionic
surfactant deflocculating agent.
In one aspect the invention comprehends a pumpable,
pseudoplastic coal-water-anionic surfactant slurry comprised
of at least about 55 percent by weight of coal, at least about
20 percent by weight of water, and at least about 0.2 percent
by weight of dry coal of an anionic organic surfactant and less
than 5 weight percent of ash. Preferably, the deflocculating
agent is in the presence of a deflocculating enhancing amount
of an alkali metal carbonate, hydroxide or silicate.
Also disclosed is a method for preparing the novel
deflocculated pseudoplastic coal-water-anionic organic surfactant
slurry. The invention also relates to utilizing the slurry as
a fuel for generation of heat energy in a suitable atomizer of
a burner of a furnace, and for other uses, to all of which uses
the slurry is delivered by pipeline and conveying means for the
slurry, such as pumps.
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A pseudoplastic fluid is one whose apparent Viscosity
or consistency decreases with increasing rate of shear. In a
shear stress vs shear rate diagram, as shown in Fig. 1 of the
drawing, the curve for a pseudoplastic fluid shows a non- -
linearly decreasing shear stress w;`th 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
plasticity. The lower the yield stress and the more pseudoplas-
tic, the more pumpable such a fluid would be.
In general the flow curve is a straight line on a
logarithmic plot and can be defined by
T = K fdu~ n where N ~1, u is velocity and r is distance.
~dr~
The apparent viscosity of the fluid is given by
ua = K (du) n-l. ;
- In a plot of logarithm of viscosity versus logarithm
o shear rate, as shown in Fig. 2, the pseudoplastic line is
seen to lie below that of a Newtonian fluid. Coal-water-anionic
organic surfactant slurries of the present invention provide
viscosity-shear rate diagrams which approximate the pseudoplas-
tic li~e in Fig. 2. Procedures for determining viscosities and
shear rates are well-known and need not be described herein in
detail.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The novel coal-water-anionic organic surfactant
slurry to which the invention relates comprises finely-divided
particles of coal such as those used in most known coal-water
slurries which can be conveyed by known pumping means, such as
piston or screw pumps. The coal used in the slurry can be any
coal suitable for pulverizing to a particle size of 50 ~m or
finer. However, particles of coal of greater or lesser initial
size can be used to obtain the benefits of the invention.
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Particles of coal of 10 ~m or less in average diameter are more
advantageous than particles of larger sizes. Coal having average
diameter paxticles of 1 ~m or less are especially preferred for
practice of the invention, in order to enhance de-ashing of the
coal by flocculation-flotation process steps and to enhance
deflocculation while retaining pseudoplastic rheology of the
coal-water slurry product of the invention.
The kind of coal used for practice of the invention
is not critical. Coals found in the United States, particularly
low volatile bituminous coals, from West ~irginia or Montana
fields, have been used and are preferred. However, anthracite,
semi~anthracite, medium and high-volatile bituminous, sub-bit-
uminous and lignite coals all may advantageously be used to
practice the invention.
The coal used to prepare the coal-water slurry can
be obtained in finely-divided form by cleaning and pulverizing
larger sized coal to the desired particle sizes. Preferably,
the coal content of the pulverized coal is enriched by known
clay and mineral separation processes to obtain a coal of low
ash content, e.g. under 5 %. However, the ash content of
the coal may be higher or lower than 5 %, e.g. from 0.5 %
to 10 % while permitting the benefits of the invention to
be obtained.
The coal for use in the process can be obtained in
a dry or wet form and mixed with water to form a coal-water
slurry. Preferably the coal is wet milled in known ways to
prevent dust and explosion hazards. The wet milled coal can
be mixed with sufficient additional water to make a mixture
which, when it is made pseudoplastic according to the invention,
will be readily pumpable in a pipeline. Usually, the water
content of the coal-water slurry product will be in the range
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of about 20% to 55~ ~y weiqht o$ slurry. Preferably, the water
content will be from 22% to 45~ by weight.
The coal-water-anionic organic surfactant slurry
hereof is prepared by adding to a coal~water slurry consisting
of coal and water an amount of an anionic surfactant e*fective
to deflocculate the pulverized coal particles to a pseudoplastic
rheological state at high solids content and to maintain the
particles in dispersed, or deflocculated, form in the water phase
of the slurry during storage and pumping to an atomizer of a
coal-water slurry burner or other use means.
The anionic organic surfactant which is used to
prepare the pseudoplastic coal-water-anionic organic slurry may
be any anionic organic surfactant which is effective to produce
a high-solids content coal-water slurry with the necessary pseu-
doplastic rheological properties. Economics of coal-water slurry
preparation, storage, conveying and atomization dictate that as
high a solids content coal as is practical be utilized. Accord-
ingly, those anionic organic surfactants which provide a coal-
water slurry with coal content of at least 55~ are preferably
used.
The surfactant to be used can be selected by experi-
me~tal tests to determine those most suitable of those available
at a particular time and place where the invention is to be
practiced. In making a selection of a suitable surfactant, one
can use a coal-water slurry containing about 55 to 80 weight
percent of coal. A viscometer, such as a Brookfield LVT visco-
meter, is used to measure the viscosity of the slurry versus
spindle speed in centipoise (cps). The viscosities at a con-
stant revolutions per minute (rpm) are measured for different
amounts of surfactant in a constant amount of coal slurry until
an optimum decrease in viscosity is obtained. Suitable surfac-
tants will produce a sharp reduction in viscosity. The viscosi-
ties are then plotted to make deflocculation curves, such as
those shown in Figs. 3, 4, and 5
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Examples of anionic orc3anic suxfactants which pro-
vide desired pseudoplastic rheological properties in coal-water
slurries containing about 55 to 80 weight ~ of coal are shown
in Table 1. In some cases, mixtures of the surfactants can
be beneficially used.
TABLE 1
Anionic Organic S`urfactant Trademark Form % conc.
2-ethylhexyl polyphosphoric Strodex
ester acid anhydrideMO-100 Liquid 100
10 Potassium Salt of Strodex
MO-100 MOK-70 Paste 70
Complex organic polyphos- Strodex
phoric ester acid anhydride MR-100Liquid 100
" " Strodex
SE-100 Liquid 100
" " Strodex
P-100 Liquid 100
" " Strodex
PK-90 Liquid 90
20 Potassium salt of complex Strodex
organic polyacid anhydride MRK-98Liquid 98
" " Strodex
SEK-50 Liquid 50
" Strodex
PSK-58 Liquid 58
" " Strodex
V-8 Liquid 85
Sodium salt of a condensed Lomar DPowder 86-
mono n~phthalene sulfonic Lomar NCO 90
30 acid Lomar PW
Sodium salt of a condensed
mono napthalene sulfonic Lomar LSPowder 95
acid
Ammonia salt of a condensed
mono napthalene sulfonicLomar OWA Powder 89
acid
Solution of sodium salt of
a condensed mono napthalene Lomar PL Liquid 45
sulfonic acid
40 (Unknown)Hydrodyne-
Aquadyne
Strodex is a trademark of Dexter Chemical Corporation.
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Lomar is a trademark of Diamond Shamrock Process
~hemicals, Inc.
Hydrodyne-Aquadyne is a trademark of Aquadyne
Company. The anionic character o~ this surfactant is confirmed
by its infrared spectra, which closely resembles those of
Strodex PK90 and Strodex V-8.
Other suitable anionic organic surfactants can be
selected from those listed in McCutcheonls, ~etergents &
Emulsifiers North American, 1976 annual edition, McCutcheon
Division, MC Publishing Co., Ridgewood, N. J. 07451 and in
Encyclopedia of Surface-Active Agents, J-P. Sisley, Chemical
Publishing Company, Inc., New York, New York (1964, Vol II).
In contrast to the anionic organic surfactants
useful in the practice of the invention, the following organic
compounds were tested and found unsuitable as effective defloccu-
lants for forming a pseudop~astic coal-water slurry: benzene,
kerosene, sodium acetate, stearic acid, oxalic acid, oleic
acid, tannic acid, n-butyl alcohol, isobutyl alcohol, Nalco
334, (only slightly anionic), Nalco 321 (cationic amine), Nalco
345 (polyol ester, nonionic), Nalco 393 (Zn with inorganic
dispersant), Nalco 918 ~inorganic polyphosphate).
Nalco is a trademark of National Aluminate Company.
The following inorganic compounds also were found
unsuitable as effective deflocculants: KF, Li2CO3 Mg(NO3)2
NaNO3 Na2SO4 and Calgon (trademark for sodium hexametaphosphate).
The following alkali inorganic compounds were found
effective to enhance the deflocculant activity of the anionic
organic surfactant: K2CO3 NaOH, and Na2SiO3 9H20. When
used, the alkali material preferably is added before the anionic
organic surfactant is added to the slurry but this order is
not essential. Mixtures of the alkali materials also can be
used.
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The amount of anionic organic surfactant defloccu-
lant used can be determined e~perimentally as described above
for a particular coal-water slurry to convert it to a pseudo-
plastic mass. The amount will ~ary depending upon such factors
as the concentration of the coal, the particle size and particle
size distribution, the amount of ash, i.e. clays and other
minerals present, the temperature of the mass, the pH, and the
anionic organic surfactant and its concentration. Specifically,
in determining the amount of anionic organic surfactant needed,
a series of measurements are made of viscosities versus shear
rates as described above for a series of coal-water slurries
containing a range of amounts of surfactant for a constant
amount of coal-water slurry. The data can be plotted on a
-~ logarithmic chart as shown in Fig. 2 and used as a guide to the
optimum quantities of surfactant to use.
Fig. 3 shows semi-logarithmic plots of deflocculation
cu~ves obtained with varying amounts of sodium salt of condensed
mono naphthalene sulfonic acid (Lomar PWA and Lomar PW) and of
the ammonia salt of said sulfonic acid (Lomar D) dispersed in
water in parts of surfactant per 100 parts of coal (dry basis)
in a coal-water-anionic organic surfactant slurry containing
55 wgt. ~ of West Virginia coal. Pseudoplasticity is retained
at full deflocculation when about 0.4 to 0.7 gm of the anionic
surfactant is present per 100 gms of dry coal in a deflocculated
coal slurry containing 55 weight % of coal.
Fig. 4 similarly shows semi-logarithmic plots of
deflocculation curves obtained with varying amounts of potassium
salt of complex organic polyphosphate ester acid anhydride
(Strodex V8 and Strodex PK-90) and of Hydrodyne-Aquadyne dis-
persed in water in ml. of surfactant per 100 parts of coal
(dry basis) in a coal-water-anionic organic surfactant slurry
containing 55 wgt. ~ of West Virginia coal slurry. It is seen
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that pseudoplasticity is retained when about 1 to 2 mls of
liquid anionic surfactant are present per 100 gms of dry coal
in a deflocculated coal slurry containing 55 weight ~ of coal.
Quantities of other anionic organic surfactants to
use can be determined similarly. In general, the flow behavior
of the slurry is controlled below the solids content or the
deflocculant addition level at which dilatency begins to occur
i.e. below the level at which viscosity increases as shear rate
increases. Pumpability of the coal-water-anionic organic sur~
factant slurry is optimum under pseudoplastic rheological con-
ditions and decreases rapidly as dilatency is approached.
As discussed above r certain alkali inorganic com-
pounds can be added to the slurry to enhance the pseudoplasticity
of the slurry in the presence of the anionic organic surfactant.
The effects of the addition of NaOH to a 55% coal-water slurry
containing varying amounts of an anionic organic surfactant,
Lomar D, a~e shown in Table 2.
TABLE 2
; ~ Lomar D Viscosity, cps
at 60 rpm
20 0.4 1.15 450
1.2 0.75 175
2.0 0.80 450
Table 2 shows a ratio of NaOH to Lomar D of
1.2:0.75 to provide an optimum low viscosity of 176 cps at
60 rpm, while retaining pseudoplasticity.
Fig. 5 shows deflocculation curves obtained using
West Virginia bituminous coal-water slurry, 67.4 wgt. ~ solids,
deflocculated with from about 0.75 to 1.05 gms of Lomar D per `
100 parts of coal (dry basis) and varying amounts of NaOH and
K2CO3. The alkali materials were prepared as 10N solutions in
water and added in various amounts by volume to the slurry. In
Fig. 5, 0 = Oml; lN = 1 ml of 10N-NaOH; 3N = 3 ml 10N-NaOH;
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~7~8
5N = 5ml 10N-NaOH; lK = 1 ml 10N-K2CQ3. It is seen from the
deflocculation curves that the use of 3 ml of 10N-NaOH pro-
vides optimum low viscosity at about 0.75 gm of Lomar D per
100 gms of coal in this coal-water-anionic organic surfactant
slurry.
EXAMPLE
The practice of the invention in an integrated
process will now be described with reference to Figs. 6 and 7
of the drawing.
Bituminous coal from West Virginia, containing
about 21% ash as mined or washed is introduced into a crusher
1 wherein it is crushed to about 2" size or less. The term
"ash" is used herein to define non-combustible content of the
coal, such as clay and various minerals. The crushed coal is
charged into a mill 2, preferably a ball mill, where it is re-
duced to a particle size of 95% ~ 30~m. The particles of finely
pulverized coal are then charged to a slurry tank 3 containing
water sufficient to maintain a solids content of about 10% by
weight. The pH of the mass in tank 3 is maintained at a pH of
10 or higher by addition of a solution of NaOH to cause defloc-
culation and separation of ash materials. Tank 3 is provided
with a high intensity agitator 4 to effect dispersion of all
particles. After about 20 minutes agitation, the slurry is
continuously pumped by pump 3a through line 7 through the hydro-
cyclone 5 and hence back to tank 3. The hydrocyclone 5 removes
the higher specific gravity minerals, preferably flocculated,
and delivers them to scrap or reprocessing. After a suitable
time of cycling the slurry through the hydrocyclone to maximize
ash removal, the valve 3B is closed and ~alve 3C opened to
filter press 6 to filter the batch from tank 3. Filtrate from
filter press 6 is recycled to tank 3. The pH of the water is
adjusted b~ addition of a solution of caustic soda (NaOH).
The partially ash-free coal thus obtained contains from about
0.5 to 10 wgt. ~ of ash. Treatment of the coal in tank 3 is,
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however, beneficial to remove at least gross amounts of the ash
content of the coal, thereby increasing the net btu value of
the coal-water slurry. The filter cake from filter 6 containing
the coal and about 25 wgt. ~ water is discharged to a second
slurry tank 8 where the cake is agitated by means of a low speed
agitator 9 operated as in tank 3. The filter cake is dispersed
in tank 8 with sufficient excess dry coal if necessary to pro-
vide a slurry containing about 20wgt. % of the coal. Aqueous
treatment of the coal for ash removal, deflocculation, and
concentration also provides a suitable vehicle for sulfur
removal.
Anionic organic surfactant, preferably Lomar D,
and a solution of 10 normal (lON) NaOH are added to tank 8.
Addition of the surfactant and NaOH solution cause defloccula-
tion of the coal in the water. The Lomar D is added at a rate
of about 1.25 parts and the NaOH at a rate of about 0.75 parts
; 10N NaOH based on 100 parts of dry coal by weight. A stable,
deflocculated pseudoplastic coal-water-anionic organic surfac-
tant slurry is formed. The slurry contains about 75 wgt. ~ of
20 partially ash-free coal, 1.25 wgt. ~ of Lomar D, 0.30 wgt. %
NaOH, the remainder being water.
The pseudoplastic coal-water-anionic organic
surfactant slurry is discharged from tank 8 to a storage
tank 10. Successive charges of the coal-water-anionic organic
surfactant slurry are blended continuously in tank 10, preferably
by pumping it continuously through a recycle pipeline 11 leading
from the bottom of tank 10 to the top of tank 10. Uniformity
of the coal-water-anionic organic surfactant slurry is thus main-
tained and provides slurry of a substantially uniform btu content.
Also, the recycling aids to minimize unwanted settling of the coal
in the slurry should inadequate amounts of anionic organic sur-
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~7~8
factant be use~ in a tank 8 to deflocculate the coal particles.
This is a contingency plan and should not be necessaxy. As
discussed abo~e, the amount of anionic organic sur~actant
which must be used to obtain the benefits and advantages of
the invention must be sufficient to form a pseudoplastic mass.
If an excess amount is used the mass may be dilatent and exces-
sively viscous and even unpumpable. If an inadequate amount
is used the system will be still pseudoplastic but with a high
viscosity and attendant pumping difficulties.
The blended deflocculated pseudoplastic coal-water
slurry can be pumped directly from the bottom of tank 10 to
an atomizer burner 12 of a furnace 13 used to generate heat
energy to heat water in a steam boiler or pumped to storage
tanks. Details of a typical atomizer burner for burning a
coal-water-anionic organic surfactant are shown in Fig. 7.
Net heat content of coal-water-anionic organic
surfactant slurry of the above composition of the E~ample was
determined to be about 105,000 btu/gallon of slurry when
burned in the atomizer of a gas supported burner, compared to
fuel oil which provides about 130,000 btu/gallon. In the fur-
nace, the slurry burned cleanly and efficiently with no detect-
able smoke, sparks, or odor.
The flame produced by the burning of the coal
slurry can be radiation stabilized, although it may be possible
for self-stabilization to occur at about 75~ solids content
in a properly designed burner.
Cost calculations which have been made show that
deflocculated coal-water-anionic organic surfactant slurry of
the invention can be produced in large quantities to make the
slurry competitive with oil on an equivalent heating value
basis.
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Although the invention has been described in
relation to use of the deflocculated coal-water-anionic organic
surfactant sluxry for heat generation by direct combustion, it
is also intended that the slurry of th~ invention be used in
coal gasi~ication or liquifaction processes to provide fuel
gases and other coal byproducts. Besides being useful in con-
ventional heat generating systems, this coal-water-anionic
organic surfactant slurry may provide unique properties for
MHD generators (magneto-hydro-dynamic) in as much as said alkali
ions are already present.
While the inventors hereof do not intend to be
bound by any theory as to the reasons for the advantages obtain-
ed by use of an anionic organic surfactant for deflocculating
the pulveriæed coal particles in water, they believe that like
ionic charges on the coal particles may in some way be involved
and that repellencies of the particles are enhanced by the
presence in the slurry of the anionic organic surfactant,
especially in the presence of certain alkali materials.
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 combinations of process steps discussed without
departing from the scope of the invention as defined in the
following claims.
