U.S. patent application number 12/157219 was filed with the patent office on 2008-10-02 for method for producing solid ceramic particles using a spray drying process.
This patent application is currently assigned to CARBO Ceramics Inc.. Invention is credited to Steve Canova, Thomas C. Palamara, Jimmy C. Wood.
Application Number | 20080241540 12/157219 |
Document ID | / |
Family ID | 35785758 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080241540 |
Kind Code |
A1 |
Canova; Steve ; et
al. |
October 2, 2008 |
Method for producing solid ceramic particles using a spray drying
process
Abstract
Methods for producing solid, substantially round, spherical and
sintered particles from a slurry of a calcined, uncalcined or
partially calcined raw material having an alumina content of
greater than about 40 weight percent. The slurry is processed with
spray drying methods into solid, substantially round, spherical and
sintered particles having an average particle size greater than
about 200 microns, a bulk density of greater than about 1.40 g/cc,
and an apparent specific gravity of greater than about 2.60.
Inventors: |
Canova; Steve; (Gray,
GA) ; Palamara; Thomas C.; (Eufaula, AL) ;
Wood; Jimmy C.; (Eufaula, AL) |
Correspondence
Address: |
HAYNES AND BOONE, LLP
901 Main Street, Suite 3100
Dallas
TX
75202
US
|
Assignee: |
CARBO Ceramics Inc.
Irving
TX
|
Family ID: |
35785758 |
Appl. No.: |
12/157219 |
Filed: |
June 9, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11178081 |
Jul 8, 2005 |
7387752 |
|
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12157219 |
|
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60586809 |
Jul 9, 2004 |
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Current U.S.
Class: |
428/402 ;
264/15 |
Current CPC
Class: |
C04B 35/62645 20130101;
C04B 35/6306 20130101; C04B 2235/77 20130101; C04B 35/632 20130101;
C04B 2235/528 20130101; C04B 2235/449 20130101; Y10T 428/2982
20150115; C04B 33/04 20130101; C04B 35/111 20130101; C04B 2235/5463
20130101; C04B 2235/3217 20130101; C04B 35/63 20130101; C04B
35/62655 20130101; C04B 35/6313 20130101; C04B 35/63416 20130101;
B01D 1/18 20130101; F26B 3/12 20130101; C04B 33/36 20130101; C04B
33/30 20130101; B28B 1/004 20130101; C04B 2235/5436 20130101; C04B
35/62625 20130101; C04B 35/6263 20130101; C04B 2235/5427
20130101 |
Class at
Publication: |
428/402 ;
264/15 |
International
Class: |
B28B 11/08 20060101
B28B011/08; B32B 15/02 20060101 B32B015/02 |
Claims
1. A method for producing solid sintered ceramic particles that are
substantially round and spherical comprising: preparing a slurry
having a solids content of greater than about 50% by weight, and
comprising water and a ceramic starting material, which ceramic
starting material has an alumina content of greater than about 40
weight percent; feeding the slurry to an atomizer operably
connected to a dryer; operating the atomizer to atomize the slurry
into droplets; operating the dryer to provide an air inlet
temperature in a range of from about 100.degree. C. to about
500.degree. C.; forming solid substantially round and spherical
particles by allowing the droplets to pass through the dryer and
exit through a discharge of the dryer; sintering at least a portion
of the particles discharged from the dryer at a temperature of from
about 1000.degree. C. to about 1600.degree. C. for a time at peak
temperature of from about 20 to about 45 minutes, wherein sintered,
solid, substantially round and spherical particles are formed
having an average particle size of greater than about 200 microns,
an average bulk density of greater than about 1.40 g/cc, and an
average apparent specific gravity of greater than about 2.60.
2. The method of claim 1 wherein the air inlet temperature is in a
range selected from the group consisting of from about 100.degree.
C. to about 200.degree. C., from about 200.degree. C. to about
300.degree. C., from about 300.degree. C. to about 400.degree. C.,
and from about 400.degree. C. to about 500.degree. C.
3. The method of claim 1 wherein the air inlet temperature is in a
range selected from the group consisting of from about 150.degree.
C. to about 200.degree. C. and from about 200.degree. C. to about
250.degree. C.
4. The method of claim 1 further comprising: adding a binder to the
slurry before feeding the slurry to the atomizer, wherein the
binder is added to the slurry in an amount of less than about 0.5
weight percent, by weight of the ceramic starting material.
5. The method of claim 1 further comprising: adding a binder to the
slurry before feeding the slurry to the atomizer, wherein the
binder is added to the slurry in an amount of less than about 1.0
weight percent, by weight of the ceramic starting material.
6. The method of claim 1 further comprising: adding a dispersant to
the slurry before feeding the slurry to the atomizer, wherein the
dispersant is added to the slurry in an amount of less than about
0.3% weight percent.
7. The method of claim 1 further comprising: adding a dispersant to
the slurry before feeding the slurry to the atomizer, wherein the
dispersant is added to the slurry in an amount of less than about
0.5% weight percent.
8. The method of claim 1 further comprising: adding a dispersant to
the slurry before feeding the slurry to the atomizer, wherein the
dispersant is added to the slurry in an amount of less than about
1.0% weight percent.
9. The method of claim 1 wherein the ceramic starting material is
selected from the group consisting of calcined material, uncalcined
material, partially calcined material, and mixtures thereof.
10. The method of claim 1 wherein the ceramic starting material is
selected from the group consisting of kaolin clay, bauxitic kaolin
and bauxite.
11. The method of claim 1 wherein the atomizer is selected from the
group consisting of rotary wheel atomizers, pressure nozzle
atomizers and dual fluid nozzle atomizers.
12. A method for producing solid sintered ceramic particles that
are substantially round and spherical comprising: preparing a
slurry having a solids content of greater than about 50% by weight,
and comprising water and a ceramic starting material, which ceramic
starting material has an alumina content of greater than about 40
weight percent; feeding the slurry to an atomizer operably
connected to a dryer; feeding drying air into the dryer; operating
the atomizer to atomize the slurry into droplets; forming solid
substantially round and spherical particles by allowing the
droplets to pass through the dryer; and controlling at least one of
the solids content of the slurry, the temperature of the drying air
entering the dryer, and the feed rate of the drying air entering
the dryer so as to produce solid substantially round and spherical
particles, that when sintered at a temperature of from about
1000.degree. C. to about 1600.degree. C. for a time at peak
temperature of from about 20 to about 45 minutes, have an average
particle size of greater than about 200 microns, an average bulk
density of greater than about 1.40 g/cc, and an average apparent
specific gravity of greater than about 2.60.
13. The method of claim 12 further comprising: adding at least one
additive selected from the group consisting of dispersants and
binders to the slurry; and controlling the amount of the selected
additive so as to produce the sintered, solid substantially round
and spherical particles having an average particle size of greater
than about 200 microns, an average bulk density of greater than
about 1.40 g/cc, and an average apparent specific gravity of
greater than about 2.60.
14. The method of claim 13 wherein the selected additive is a
dispersant selected from the group consisting of colloids,
polyelectrolytes, tetra sodium pyrophosphate, tetra potassium
pyrophosphate, polyphosphate, ammonium citrate, ferric ammonium
citrate and sodium hexametaphosphate.
15. The method of claim 13 wherein the selected additive is a
binder selected from the group consisting of polyvinyl alcohol,
polyvinyl acetate, methylcellulose, dextrin and molasses.
16. The method of claim 12 further comprising: adjusting a
dimension of the dryer so as to adjust at least one of the average
particle size, bulk density and apparent specific gravity of the
solid substantially round and spherical particles.
17. The method of claim 16 wherein the height of the dryer is
increased so as to increase the average particle size of the solid
substantially round and spherical particles.
18. Particles that: are solid; are substantially round and
spherical; have an average size of greater than about 200 microns;
have an average bulk density of greater than about 1.40 g/cc; and
have an average apparent specific gravity of greater than about
2.60, wherein the particles are formed by: preparing a slurry
having a solids content of greater than about 50% by weight, and
comprising water and a ceramic starting material having an alumina
content of greater than about 40 weight percent; feeding the slurry
to an atomizer operably connected to a dryer; operating the
atomizer to atomize the slurry into droplets; operating the dryer
to provide a flow of air into the dryer at an air inlet temperature
in a range of from about 100.degree. C. to about 500.degree. C.;
forming solid substantially round and spherical particles by
allowing the droplets to pass through the dryer and exit through a
discharge of the dryer; and sintering at least a portion of the
particles discharged from the dryer at a temperature of from about
1000.degree. C. to about 1600.degree. C. for a time at peak
temperature of from about 20 to about 45 minutes.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation of U.S. patent
application Ser. No. 11/178,081, filed on Jul. 8, 2005, which
claims benefit of provisional Application No. 60/586,809, filed on
Jul. 9, 2004, which are incorporated by reference in its
entirety.
BACKGROUND
[0002] Spray drying involves the atomization of a ceramic fluid
feedstock into sprays of droplets, which are dried to individual
powder particles on contact with hot air. Primarily utilized in the
ceramic tile and dinnerware industry, called the whiteware
industry, spray drying is found in many industrial applications
including electronic ceramics (semi-conductors, capacitors) and
structural ceramics (wear parts, cutting tools, biomedical
parts).
[0003] Oil and natural gas are produced from wells having porous
and permeable subterranean formations. The porosity of the
formation permits the formation to store oil and gas, and the
permeability of the formation permits the oil or gas fluid to move
through the formation. Permeability of the formation is essential
to permit oil and gas to flow to a location where it can be pumped
from the well. Sometimes the permeability of the formation holding
the gas or oil is insufficient for economic recovery of oil and
gas. In other cases, during operation of the well, the permeability
of the formation drops to the extent that further recovery becomes
uneconomical. In such cases, it is necessary to fracture the
formation and prop the fracture in an open condition by means of a
proppant material or propping agent. Such fracturing is usually
accomplished by hydraulic pressure, and the proppant material or
propping agent is a particulate material, such as sand, glass beads
or ceramic particles, which are carried into the fracture by means
of a fluid.
[0004] Described herein are methods for making solid ceramic
particles that are substantially round and spherical using a spray
drying process. When sintered, the solid ceramic particles are
suitable for use as proppant material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a diagram of a method for making sintered solid
ceramic particles that are substantially round and spherical using
a spray drying process as described herein.
[0006] FIG. 2 illustrates a drying chamber providing a combination
of co-current and counter-current flow for use in spray drying
methods as described herein.
[0007] FIG. 3 illustrates a drying chamber providing a co-current
flow for use in spray drying methods as described herein.
[0008] FIG. 4 illustrates a dimensional scale-up of drying chambers
for making solid ceramic particles that are substantially round and
spherical using a spray drying process as described herein.
DETAILED DESCRIPTION
[0009] In particular, methods for making substantially round and
spherical, solid, sintered ceramic particles having an average
particle size of greater than about 200 microns, a bulk density of
greater than about 1.40 g/cc, and an apparent specific gravity of
greater than about 2.60 are described. In certain embodiments, the
particles have an average particle size of greater than about 300
microns, or greater than about 400 microns. As used herein, the
phrase "average particle size" describes a particle size calculated
from the sieve distribution of a batch of the particles.
[0010] As used herein, the phrase "solid ceramic particle"
describes ceramic particles having an interior void that is less
than about 10% by volume of the particle. In certain embodiments,
the solid ceramic particles have an interior void that is less than
about 5% by volume of the particle.
[0011] Referring now to FIG. 1, a method for making a solid ceramic
particle that is substantially round and spherical using a spray
drying process includes slurry preparation 100, atomization 102,
contact 104, drying 106, discharge 108, and sinter 110.
[0012] In slurry preparation 100, a slurry is prepared comprising
water and a ceramic starting material having an alumina content of
greater than about 40 weight percent. The slurry is prepared by
blending, mixing, agitating or similar means known to those of
ordinary skill in the art. The ceramic starting material may be an
uncalcined ceramic material, partially calcined ceramic material,
calcined ceramic material, or combinations thereof. In certain
embodiments, the ceramic starting material is a material from which
a solid ceramic particle that is substantially round and spherical
can be made, and which contains naturally-occurring volatiles,
which volatiles may include moisture, organics and chemically bound
water (also referred to as "water of hydration"). In certain
embodiments, the amount of naturally-occurring volatiles is from
about 10 to about 40 wt. % of the ceramic starting material. In
other embodiments, the ceramic starting material is an uncalcined
clay, partially calcined clay, calcined clay, or mixtures thereof.
In still other embodiments, the ceramic starting material is a
kaolin clay, bauxitic clay, or bauxite, any of which may be
calcined, partially calcined, or uncalcined, and mixtures
thereof.
[0013] In certain embodiments, the slurry further comprises a
binder, such as polyvinyl alcohol, polyvinyl acetate,
methylcellulose, dextrin and molasses. Binders are typically
organic materials used to increase particle strength. In certain
embodiments, water can act as a binder.
[0014] In still other embodiments, the slurry further comprises a
dispersant, such as a colloid, a polyelectrolyte, tetra sodium
pyrophosphate, tetra potassium pyrophosphate, polyphosphate,
ammonium citrate, ferric ammonium citrate and sodium
hexametaphosphate. Dispersants are included to enhance the total
solids content of the slurry by reducing the slurry viscosity. The
amount of dispersant, if any, to be used in a slurry is balanced
between the ability to atomize the slurry and the ability to make
solid, spherical particles.
[0015] The relative quantities of ceramic starting material, water,
binder (if any) and dispersant (if any) in the slurry depend on the
desired properties for the solid ceramic proppant, but are limited
to those amounts that will make the slurry suitable for pumping
through a pressure nozzle or rotating wheel in atomization process
102, and will allow for the production of green particles that can
be sintered to form solid ceramic particles that are substantially
round and spherical. In certain embodiments, the slurry has a
solids content in the range of from about 50 to about 75% by
weight, while in other embodiments, the solids content is from
about 50 to about 60% by weight, or from about 60% to about 70% by
weight.
[0016] In embodiments where the slurry comprises a binder, the
amount of binder can be less than about 0.5 percent, by weight of
the dry ceramic starting material, or less than about 1.0 percent,
by weight of the dry ceramic starting material.
[0017] In embodiments where the slurry comprises a dispersant, the
amount of dispersant can be less than about 0.3 percent, by weight
of the dry ceramic starting material, less than about 0.5 percent,
by weight of the dry ceramic starting material, or less than about
1.0 percent, by weight of the dry ceramic starting material.
[0018] In atomization process 102, the slurry is fed to atomizing
equipment. Suitable atomizing equipment includes but is not limited
to a rotary wheel atomizer, a pressure nozzle atomizer and a dual
fluid nozzle atomizer. Rotary wheel, pressure nozzle and dual fluid
nozzle atomizers are known to those of ordinary skill in the art,
and include those in spray dryers commercially available from a
variety of sources, such as Niro, Inc. Nozzle design is known and
understood by those of ordinary skill in the art, e.g. K. Masters:
"Spray Drying Handbook", John Wiley and Sons, New York (1979).
[0019] Whether to use a rotary wheel, pressure nozzle, or dual
fluid nozzle atomizer depends upon properties, such as size,
distribution, and shape, desired in the final dried solid ceramic
particle along with the desired production capacity. Generally,
rotary wheel atomizers produce fine particles, while pressure
nozzles and dual fluid nozzles operated under pressure can produce
comparatively larger particles.
[0020] When a rotary wheel atomizer is used, ceramic slurry is fed
to the center of the rotating wheel of the atomizer, and moves to
the periphery of the wheel by centrifugal force. Atomization takes
place at the wheel edge. The size of droplets and the size
distribution of droplets in the resulting spray depend upon the
amount of energy imparted to the slurry and the frictional effects
between the newly formed droplets and the turbulent air flow near
the wheel. Sprays of droplets are ejected horizontally from the
wheel but quickly follow the airflow patterns created by an air
disperser, which directs the hot air down into a drying chamber in
a controlled manner. The particle size of ceramics produced in
spray dryers with rotary wheel atomizers increases with decrease in
atomizer wheel speed. The effect of feed rate is not great within
the optimum working range of the given atomizer wheel, and
fluctuations in feed rate during operation do not change the size
distribution of the ceramic powder produced. Chamber diameters used
with rotary wheel atomizers should generally be large enough to
prevent the formation of semi wet deposits at the chamber wall at
the atomizer level. In contrast, chambers of smaller diameter but
larger cylindrical height can be used with pressure nozzle and dual
fluid nozzle atomizers.
[0021] When a pressure nozzle atomizer is used, slurry is fed to
the nozzle under pressure. In the case of a dual fluid nozzle,
slurry and drying air are fed through separate nozzles. The feed of
air is pressurized, while the feed of slurry can be pressurized or
a siphon/gravity feed. In the embodiments described herein as using
a dual fluid nozzle, the slurry feed was pressurized.
[0022] The pressure energy is converted into kinetic energy, and
the slurry flows from the nozzle orifice as a high-speed film that
readily disintegrates into droplets. The droplet size produced from
a pressure nozzle atomizer or pressurized dual fluid nozzle varies
inversely with pressure and directly with feed rate and feed
viscosity. The capacity of a pressure nozzle or pressurized dual
fluid nozzle varies with the square root of pressure. In certain
embodiments where high feed rates and/or high-capacity spray drying
is desired, multi-nozzle systems are used.
[0023] Turning now to contact 104, a spray of droplets of slurry
exiting the atomizing equipment meets hot drying air entering a
drying chamber. How the droplets and drying air are initially
contacted, and how the droplets/particles move throughout the
drying chamber can generally be described as either co-current,
counter-current, or a combination thereof. In certain embodiments,
such as the one illustrated in FIG. 2, a drying chamber providing a
combination of co-current and counter-current flow is illustrated
in use with a pressure nozzle atomizer.
[0024] FIG. 2 is a simplified diagram of a spray drying apparatus
comprising a drying chamber 204 and a pressure nozzle 202. Spray
dryers typically include additional components, which need not be
detailed herein, as spray dryers and their components are known to
those of ordinary skill in the art. In FIG. 2, slurry is fed from a
feed source 200 through a pressure nozzle 202. Although only one
pressure nozzle is illustrated in FIG. 2, multiple nozzles can be
used. Various types of equipment suitable for feeding a slurry are
known to those of ordinary skill in the art, and can include, for
example, a feed pump with or without a filter. The pressure nozzle
202 atomizes the slurry into droplets and sprays the droplets
upward into the dryer chamber 204, which is illustrated by arrows
A. Hot air is fed into the drying chamber 204 from an air source
206, through an inlet 208 and enters the drying chamber 204 where
it contacts the slurry droplets. Thus, the hot air enters from a
point above the point at which the slurry is sprayed into the
drying chamber, and flows in a generally downward direction in the
chamber. Initially, the slurry droplets flow in a generally upward
direction in the drying chamber, thereby establishing a
counter-current flow. At some point, however, the droplets will
exhaust their vertical trajectory, and begin to flow in a generally
downward direction in the chamber, thereby establishing a
co-current flow. Droplets in a drying chamber such as that
illustrated in FIG. 2 have an extended vertical trajectory, which
allows a longer airborne time for drying. Although FIG. 2
illustrates a pressure nozzle atomizer in use with a combination
co-current and counter-current drying chamber, such drying chambers
can also be used with rotary wheel atomizers and dual fluid nozzle
atomizers.
[0025] In certain embodiments, such as that illustrated in FIG. 3,
a co-current drying chamber is used with a pressure nozzle
atomizer. FIG. 3 is a simplified diagram of a spray drying
apparatus comprising a drying chamber 304 and a pressure nozzle
302. Slurry is fed from a feed source 300 through a pressure nozzle
302. The pressure nozzle 302 atomizes the slurry into droplets and
sprays the droplets in a generally downward direction (illustrated
at "A") into the dryer chamber 304. Hot air is fed into the drying
chamber 304 from an air source 306, and flows into the drying
chamber 304 in a generally downward direction (illustrated at "B").
Thus, the hot air and the slurry droplets flow in a generally
downward direction in the chamber, thereby establishing a
co-current flow. Although FIG. 3 illustrates a pressure nozzle
atomizer in use with a co-current drying chamber, co-current drying
chambers can also be used with rotary wheel atomizers and dual
fluid nozzle atomizers.
[0026] Various types of equipment suitable for feeding hot air into
the drying chamber for drying of the droplets are known to those of
ordinary skill in the art, and can include, for example, a heater
with or without an air filter. In drying 106, green ceramic
particles form as moisture is evaporated from the droplets. As the
slurry is sprayed into drying chamber 204 and contacts hot drying
air, evaporation from the surface of the droplet occurs and a
saturated vapor film forms at the surface of the droplet.
Dispersants and binders, if present, are soluble. Thus, when a
dispersant and/or binder is present, each atomized spray droplet
contains both insoluble ceramic material and soluble additives.
During the evaporation phase of spray drying, the soluble binding
materials coat themselves in a film on the droplet surface.
[0027] As drying continues, moisture toward the interior of the
droplet evaporates. According to the methods described herein,
moisture from the interior of the droplet is evaporated at least in
part by diffusion through the solid particles packed in the
droplet, toward the droplet surface, and then through the film on
the droplet surface. As evaporation of moisture from the droplet
interior occurs, the film on the droplet surface grows inward
toward the droplet interior.
[0028] Droplet surface temperatures are low in spite of the
relatively higher inlet air temperature of the drying air.
Evaporation takes place initially under constant-rate conditions,
but then the rate falls as the droplets approach a final residual
moisture content condition. Since the droplets contain undissolved
solids, the drying profile features a significant constant-rate
period that contributes to the particle sphericity. During drying,
the spray droplet size distribution changes as droplets change size
during evaporation of moisture. Coalescence of droplets and
particles can also occur, and may be due to the turbulent air flow
pattern in the drying chamber and the complex distribution of
temperature and humidity levels.
[0029] Because the droplets generally do not rotate as they are
projected through the drying chamber, one side of the droplet can
be exposed to air from the inlet that is hotter than the air to
which the other side of the droplet is exposed (referred to herein
as the "hot side" and the "cool side", respectively). In such
instances, evaporation is faster on the hot side, and the film that
forms on the surface of the droplet thickens more rapidly on the
hot side than on the cool side. Liquid and solids in the droplet
migrate to the hot side. At this point, it would be expected that
the cool side would be drawn inward, which would result in a hollow
green particle with a dimple, rather than the solid green particles
described herein. However, according to the methods described
herein, the particles are solid rather than hollow because of one
or more of the following factors: solids content in the weight
percents described herein, solubles content (dispersant and/or
binder) in the weight percents described herein, and air inlet
temperatures in the ranges as described herein.
[0030] Regarding the solids content, slurries having solids
contents greater than about 50 weight percent can be used to
produce solid substantially round and spherical particles as
described herein. According to certain embodiments, slurries having
a solids content of about 60% to about 70% by weight can be used to
produce solid substantially round and spherical particles.
[0031] Regarding the solubles content, binders increase slurry
viscosity, which can lead to the need to reduce the solids content
in order to maintain a slurry that can be atomized. Lower solids
content, however, can lead to a particle that is not solid. As for
dispersants, dispersants allow more rapid movement of solids to the
surface of the particle, which can also lead to a particle that is
not solid. Thus, the solubles content in a slurry (amounts of
additives such as binders and dispersants) should be balanced
against the solids content of the slurry. Preferably, the least
amount of binder and/or dispersant, as determined by the need to
adjust viscosity of the slurry, is used.
[0032] Regarding the air inlet temperatures, the temperature of the
air entering a drying chamber is controlled according to methods
described herein. Thus, in certain embodiments, the air inlet
temperature is in a range of from about 100.degree. C. to about
200.degree. C., or from about 200.degree. C. to about 300.degree.
C., or from about 300.degree. C. to about 400.degree. C., or from
about 400.degree. C. to about 500.degree. C. In other embodiments,
the air inlet temperature is in a range of from about 150.degree.
C. to about 200.degree. C. or from about 200.degree. C. to about
250.degree. C. Preferably, temperatures in the lower end of such
ranges are used in order to slow the rate of drying of the
particles, which in turn contributes to the production of green
ceramic particles that can be sintered to produce solid ceramic
particles that are substantially round and spherical.
[0033] Referring again to FIG. 1, discharge 108 includes separation
and discharge of green ceramic particles from the dryer chamber. In
certain embodiments, a two-point discharge system is used. In a
two-point discharge system, primary discharge of the coarsest
fraction of the green ceramic particles is achieved from the base
of the chamber and discharge of the finer fraction is achieved from
the base of a cyclone and baghouse system. In certain other
embodiments, a single-point discharge system is used. In a
single-point discharge system, recovery of the green ceramic
particles is accomplished from the dryer chamber. For example, in
the schematic illustrated in FIGS. 2 and 3, the green ceramic
particles are discharged from the drying chamber into a discharge
210 and 310 at least in part under the influence of gravity.
[0034] In addition to the components illustrated in FIGS. 2 and 3,
suitable drying arrangements can further include fans and ducts,
exhaust air cleaning equipment (cyclones, baghouses, scrubbers),
and control instrumentation. Such further components and equipment,
and their use in a spray drying method as described herein, are
known to those of ordinary skill in the art.
[0035] After discharge 108, the green ceramic particles are then
sintered 110 using conventional sintering equipment to form solid
ceramic particles that are substantially round and spherical.
Sintering and equipment to perform sintering are known to those of
ordinary skill in the art. For example, see U.S. Pat. No. 4,427,068
to Fitzgibbon. In certain embodiments, sintering is performed at a
temperature in the range of from about 1000.degree. C. to about
1600.degree. C. for a time in the range of from about 20 to about
45 minutes at peak temperature.
[0036] The following examples are illustrative of the methods and
particles discussed above.
EXAMPLE 1
[0037] Referring now to Table 1 below, the results of nine test
runs that produced substantially round and spherical solid ceramic
particles according to the methods disclosed herein are reported.
Values reported in Table 1 as "n/a" were not determined.
[0038] Nine slurries having the Slurry Properties reported in Table
1 were prepared by and obtained from CARBO Ceramics, Inc.,
("CARBO") Eufaula, Ala. Generally, the slurries were prepared by
agitating an uncalcined bauxitic kaolin clay with water and a
dispersant in a Denver attrition scrubber to achieve a slurry
having the reported solids content. The clay had an alumina content
of greater than about 50 weight percent, and was a blend of clay
mined in the Eufaula, Alabama area. The dispersant used was an
ammonium polyacrylate commercially available as Rhone Poulenc
Colloid 102. Polyvinyl alcohol (PVA) having a molecular weight of
100,000 Mn, which was obtained from Air Products and Chemicals Inc
under the tradename Airvol was added to the slurries as obtained
from CARBO for sample nos. 5 and 6. The solids content reported in
Table 1 was determined using a Sartorius moisture balance at
160.degree. C. for 30 minutes. The viscosity data reported in Table
1, (which is reported in centipoises ("cps") at a particular RPM),
was determined using a Brookfield viscometer with a number 2
spindle, which is commercially available from Brookfield
Engineering Laboratories, Middleboro, Mass. The Brookfield
viscometer was operated according to the procedures provided for
its operation.
[0039] The slurries were atomized according to the Atomization
conditions reported in Table 1. Each slurry was fed to a pressure
nozzle atomizer at the temperature and feed rate, and under the
atomization pressure, reported in Table 1. The particular atomizer
used was provided with a Niro Nozzle Tower pilot plant, which had a
drying chamber of 2.55 meters in diameter and 5.95 meters in
cylindrical height with an overall spray height of 9 meters. The
nozzle design was adjusted for each run as reported in Table 1,
where the alpha indicator "AA" describes chamber design of the
nozzle and the numeric indicator "#.#" describes the diameter
(millimeters) of the nozzle orifice. Such alpha and numeric
indicators are known and understood by those of ordinary skill in
the art. The Duration reported in Table 1 indicates the time that
the slurry was pumped at the indicated rate in order to make
droplets of the slurry from the particular nozzle used.
[0040] As the atomized droplets of slurry exited the pressure
nozzle, they were exposed to the Drying Conditions reported in
Table 1. Hot air was fed to the drying chamber of the Niro Nozzle
Tower pilot plant at the reported rate, which was measured with a
hot wire anemometer. The reported inlet and outlet temperatures of
the drying chamber were determined with thermocouples. As moisture
evaporated from the droplets due to contact with the hot air feed,
green ceramic particles were formed having the Green Properties
reported in Table 1. The reported residual volatiles % was
determined with a Mettler moisture analyzer at 200.degree. C. for
30 minutes, and indicates moisture that did not evaporate from the
particle during drying. The poured density represents that amount
of green particles that filled a container of known volume, while
the tapped density represents that amount of green particles that
filled a container of known volume with tapping of the container as
it was filled.
[0041] The green particles were sintered in a static kiln to
produce substantially round and spherical solid ceramic particles.
Sintering was achieved using a heating rate of 12.degree. C./min to
a peak temperature of 1510.degree. C. with a 30 minute hold at peak
temperature. Sintered Properties of the sintered solid ceramic
particles such as size, grain fineness number, bulk density,
apparent specific gravity and crush strength are reported below.
The bulk density, apparent specific gravity and crush strength were
determined using API Recommended Practices RP60 for testing
proppants.
TABLE-US-00001 TABLE 1 Sample No. 1 2 3 4 5 6 7 8 9 Slurry
Properties: Solids (wt %) 59.2 59.6 60.4 59.7 59.6 59.2 61.1 59.8
59.3 Binder (PVA) (wt %) 0 0 0 0 0.1* 0.2* 0 0 0 Dispersant (wt %)
0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Density (g/cc) 1.58 1.58 1.59
1.57 1.59 1.58 1.59 1.60 n/a Viscosity (cps) 6 RPM 775 200 1375 625
875 475 425 225 500 12 RPM 638 163 1000 450 650 488 350 200 438 30
RPM 440 115 505 315 395 305 255 140 290 60 RPM 335 98 400 250 285
230 200 118 235 Atomization Conditions Temperature of slurry 23 22
22 23 23 22 23 22 22 .degree. C. Feed Rate of slurry 211 254 254
n/a 190 233 n/a 288 220 (kg/hr) Atomization Pressure 420 440 600
460 480 440 600 500 500 (psig) Nozzle Type SC 1.6 SC 1.6 SB 1.4 SB
1.4 SB 1.4 SB 1.4 SB 1.5 SB 1.4 SB 1.4 Duration (min.) 24 35 8 27
34 35 12 11 66 Drying Conditions: Drying Air Rate 2930 3080 3000
3080 3090 3030 2730 2850 2670 (kg/hr) Inlet Air Temp. .degree. C.
231 276 221 220 210 210 260 209 231 Outlet Air Temp. .degree. C.
118 115 116 110 101 102 126 101 105 Green Properties: Residual
Volatiles, % 5.35 0.98 3.15 2.71 0.61 0.65 10.9 3.0 1.35 Poured
Density, g/cc 0.81 0.78 0.81 0.79 0.81 0.79 0.88 0.80 0.80 Tapped
Density, g/cc 0.86 0.85 0.86 0.84 0.86 0.85 0.91 0.87 0.85 Particle
Size, microns 90% less than 619 500 585 567 530 502 n/a 578 570 50%
less than 413 292 353 349 293 306 n/a 357 351 10% less than 230 171
213 200 175 188 n/a 209 186 Product Weight, kg 49.5 72 12.5 51 74
72 26 24 140.5 % Retained on Sieve U.S. Mesh No. (or pan) 30 5.0
0.4 5.0 0.9 0.1 0.0 31.9 0.8 0.5 40 34.4 7.9 23.7 20.4 4.4 1.4 31.6
16.8 7.6 50 32.2 31.4 32.0 35.0 26.1 20.9 20.7 36.9 32.6 70 16.0
27.3 22.0 21.8 30.6 32.9 9.3 23.2 35.3 100 8.8 19.7 12.2 14.0 24.4
28.3 4.6 14.4 14.4 140 2.6 8.0 3.5 5.0 9.2 10.4 1.3 5.1 200 0.6 3.1
1.0 1.7 3.1 3.3 0.3 1.6 8.7 270 0.2 1.5 0.4 0.8 1.5 2.0 0.2 0.8 pan
0.1 0.7 0.2 0.4 0.6 0.7 0.1 0.3 0.9 Avg. Size, microns 387 277 354
327 256 236 480 319 285 (including pan material) Sintered
Properties: Sieve, U.S. Mesh 30 0.6 0.1 0.6 0.1 0.0 0.0 12.5 0.1
0.0 40 8.6 0.8 7.0 1.7 0.2 0.1 26.9 1.7 0.8 50 38.8 14.6 29.1 23.9
10.1 4.4 30.5 25.1 12.9 70 28.5 36.1 31.9 35.2 33.3 30.8 17.0 36.3
34.6 100 16.8 30.0 22.2 25.2 34.0 39.4 9.4 23.9 32.2 140 5.0 11.3
6.4 8.9 14.3 17.0 2.7 8.3 12.8 200 1.3 3.9 1.7 2.8 4.6 5.0 0.7 2.7
4.1 270 0.4 2.3 0.8 1.5 2.6 2.5 0.3 1.3 2.1 pan 0.1 1.0 0.3 0.7 0.9
0.8 0.1 0.6 0.5 Avg. Size, microns 300 224 277 247 209 195 395 251
219 (including pan material) Grain Fineness Number 51.9 67.1 55.9
61.6 71.1 74.4 42.1 60.5 68.3 (GFN) (does not include pan material)
Grain Fineness 52.2 69.5 56.6 63.3 73.2 76.2 42.4 61.9 69.5 Number
(GFN) (includes pan material) Bulk Density 1.53 1.39 1.50 1.47 1.44
1.39 1.52 1.46 1.46 (g/cc) Apparent Specific 2.76 2.70 2.77 2.72
2.74 2.66 2.74 2.71 2.74 Gravity (ASG) Crush on -50/+140: 7500 psi
% Crush 4.4 9.6 5.2 5.5 6.4 9.5 5.1 6.7 5.2 10,000 psi % Crush n/a
12.3 5.9 7.5 9.3 12.8 12.3 7.9 6.6 *PVA added after slurries
received from preparation site.
[0042] Slurries having higher solids loading, (for example, Sample
Nos. 3 and 7), produced larger sized particle, by GFN and by
average particle size. Sample Nos. 3 and 7 also had a higher
viscosity, and produced the 2nd and 3rd coarsest particle size
materials by GFN and average particle size. In contrast, slurries
having higher total solubles, (for example, Samples Nos. 5 and 6,
which included binder), produced the smallest average particle
sized material with highest GFN (which also indicates smaller
particles were produced). Sample No. 7 produced the largest
particles, and it is further noted that of the nine samples, Sample
No. 7 also contained the highest residual volatiles, which
indicates the free water content of the particles discharged from
the drying chamber. The residual volatile content of Sample No. 7
indicates that Sample No. 7 was exposed to a reduced drying rate as
compared to those samples discharged from the drying chamber with
lower residual volatile contents (for example, Samples Nos. 5 and
6). Thus, a reduced drying rate should contribute to the production
of ceramic particles having properties as described herein.
EXAMPLE 2
[0043] Referring now to Table 2 below, the results of five test
runs that produced substantially round and spherical solid ceramic
particles according to the methods disclosed herein are reported.
Values reported in Table 2 as "n/a" were not determined.
[0044] Five slurries having the Slurry Properties reported in Table
2 were prepared by agitating an uncalcined bauxitic kaolin clay
with water and a dispersant in a high shear Cowles dissolver to
achieve a slurry having the reported solids content. The clay had
an alumina content of greater than about 50 weight percent, and was
obtained from JF Blecher. The dispersant was sodium
hexametaphosphate, and was included in each slurry in an amount of
about 0.15 weight percent of the dry weight of the clay used to
make the slurry. Sodium hexametaphosphate is commercially available
from Innophous Chemicals Inc. An additional 120 grams of sodium
hexametaphosphate was added to Sample Nos. 4 and 5. Ammonium
hydroxide was added to each slurry in an amount sufficient to
provide the slurries with a pH of about 9.5. No binder other than
water was used in any of the slurries.
[0045] The slurry solids content reported in Table 2 was determined
using a Ohaus MB45 moisture balance at 190.degree. C. until all
physical moisture was eliminated.
[0046] The viscosity data was determined using a Brookfield RVF
viscometer with a number 1 spindle @ 20 rpm, which is commercially
available from Brookfield Engineering Laboratories, Middleboro,
Mass. The Brookfield viscometer was operated according to the
procedures provided for its operation.
[0047] Each slurry was fed to a dual fluid nozzle at ambient
temperature, and under the atomization pressure, reported in Table
2.
[0048] The same nozzle design was used for each sample. The nozzle
type was an Air Atomizing Nozzle 1/2JBC, commercially available
from Spraying Systems, Inc. The nozzle was configured with a round
spray, external mix, spray set up no. SU 70, and pressure set up,
according to Spraying Systems Catalog 60B Express (2000), which is
a text available to those of ordinary skill in the art for
operation of Spraying Systems nozzles. With an external mix, the
air inlet for a drying chamber is not within a stream of incoming
slurry. The particular dual fluid nozzle atomizer used was used in
a pilot tower unit, which had a drying chamber of 1.524 meters in
diameter, 4.267 meters in cylindrical height, and a drying volume
of 8.59 cubic meters. The overall spray height was 5.587 meters.
The drying chamber used in this Example 2 was obtained from Drytec
North America LLC, Olympia Fields, Ill.
[0049] As the atomized droplets of slurry exited the pressure
nozzle, they were exposed to the Drying Conditions reported in
Table 2. Hot air was fed to the drying chamber at the reported
rate, which was measured using the pressure drop across the cyclone
vessel. The reported inlet and outlet temperatures of the drying
chamber were determined with type K thermocouples.
[0050] As moisture evaporated from the droplets due to contact with
the hot air feed, green ceramic particles were formed having the
Green Properties reported in Table 2. The reported residual
volatiles % was determined with a CSC moisture analyzer based on
complete moisture loss on drying, and indicates moisture that did
not evaporate from the particle during drying. The poured density
represents that amount of green particles that filled a container
of known volume, while the tapped density represents that amount of
green particles that filled a container of known volume with
tapping of the container as it was filled.
[0051] Green particles having a sieve size of U.S. mesh 40/270 were
sintered in a CM Rapid Temperature static lab kiln to produce
substantially round and spherical solid ceramic particles.
Sintering was achieved using a heating rate of 17.degree. C./min to
a peak temperature of 1500.degree. C. with a 30 minute hold at peak
temperature. Sintered Properties of the sintered solid ceramic
particles such as size, grain fineness number, bulk density,
apparent specific gravity and crush strength are reported
below.
[0052] The bulk density was determined according to ANSI B74-4-1992
procedures, and the apparent specific gravity and crush strength
were determined using API Recommended Practices RP60 for Testing
Proppants.
TABLE-US-00002 TABLE 2 Sample No. 1 2 3 4 5 Slurry Properties:
Solids (wt %) 68.8 68.8 68.8 68.8 68.8 Dispersant (wt %) 0.15 0.15
0.15 0.15 + 120 g 0.15 + 120 g Density (g/cc) n/a n/a n/a n/a n/a
Viscosity (cps) at 20 RPM 424 424 424 274 274 Atomization
Conditions Atomization Pressure (psig) 120 120 120 120 120 Drying
Conditions: Drying Air Rate N/A N/A N/A N/A N/A Inlet Air Temp.
.degree. C. 172 156 186 153 175 Outlet Air Temp. .degree. C. 129
118 135 118 129 Green Properties: Residual Volatiles, % 13.6 12.7
11.2 10.9 8.6 Poured Density, g/cc 1.01 1.02 1.03 .96 .98 Tapped
Density, g/cc 1.06 1.06 1.08 1.02 1.05 Particle Size, microns 90%
less than 595.2 666.9 648.2 648.6 510.3 50% less than 243.6 315.8
281.8 299.1 57.5 10% less than 5.3 4.0 3.6 5.0 1.5 % Retained on
Sieve U.S. Mesh No. (or pan) 30 29.2 34.8 35.7 30.0 21.9 40 17.9
18.4 16.4 18.3 17.3 50 16.3 15.8 14.2 16.2 17.8 70 13.5 12.1 11.5
13.0 15.8 100 9.8 8.4 8.8 9.8 12.7 140 5.3 4.5 4.8 5.6 6.9 200 2.6
2.7 2.7 2.6 3.2 270 2.4 1.7 2.5 1.8 1.9 pan 3.0 1.6 3.4 2.6 2.5
Avg. Size, microns (including 406 435 426 411 374 pan material)
Sintered Properties (40/270 material was sintered): Sieve, U.S.
Mesh 30 0.1 0.0 0.0 0.0 0.0 40 6.9 7.8 7.5 6.9 6.6 50 29.6 29.9
30.2 29.4 31.3 70 25.0 27.1 26.1 26.9 26.8 100 19.2 18.6 17.8 18.5
16.5 140 10.7 9.4 9.8 10.4 10.6 200 4.8 4.1 4.6 4.8 4.9 270 2.7 2.1
2.7 2.2 2.4 pan 1.1 1.0 1.2 0.9 0.9 Avg. Size, microns (including
262 269 266 264 266 pan material) Grain Fineness Number (GFN) 63.4
60.8 62.1 62.2 62.1 (does not include pan material) Bulk Density
(g/cc) 1.51 1.46 1.47 1.48 1.48 Apparent Specific Gravity 2.74 2.74
2.76 2.75 2.74 (ASG) Crush on -50/+140: 7500 psi % Crush 9.6 10.5
12.1 9.7 11.5
[0053] A comparison of Sample No. 2 to Sample No. 3 indicates that
when the outlet air temperature (and therefore also the inlet air
temperature) of the drying chamber was increased, (118.degree. C.
in No. 2 to 135.degree. C. in No. 3), the average green particle
size decreased from 435 to 426 microns. A comparison of Sample Nos.
4 and 5 indicates that when the outlet air temperature (and
therefore also the inlet air temperature) of the drying chamber was
increased, (118.degree. C. in No. 4 to 129.degree. C. in No. 5),
the average green pellet size decreased from 411 to 374 microns.
Those of ordinary skill in the art understand that a higher outlet
air temperature of a drying chamber as described herein indicates a
higher inlet air temperature. The reduction of inlet air
temperature as between Sample Nos. 2 and 3, and between Sample Nos.
4 and 5 indicate that larger particles can be produced with lower
inlet air temperatures.
[0054] A comparison of Sample Nos. 2 and 4 indicates that when
additional dispersant is present (No. 4 contained 120 g more
dispersant than No. 2, and therefore also had a lower viscosity
than No. 2), the average green pellet size decreased from 435 to
411 microns. The additional binder and lower viscosity of Sample
No. 4 as compared to Sample No. 2 indicates that larger particles
can be produced with less binder and higher viscosity (i.e., Sample
No. 2.)
[0055] In addition, the bulk densities and ASGs reported in Table 2
indicate that at least a portion of the sintered particles were
solid.
[0056] Further, the values reported in Table 2 show that particles
having a size, a bulk density, an apparent specific gravity and a
7500 psi crush strength suitable for use as propping material may
be produced from slurries as described herein, and processed with
spray dryer technology.
EXAMPLE 3
[0057] Referring now to Table 3 below, the results of seven test
runs that produced substantially round and spherical solid ceramic
particles according to the methods disclosed herein are reported.
Values reported in Table 3 as "n/a" were not determined.
[0058] Seven slurries having the Slurry Properties reported in
Table 3 were prepared by agitating an uncalcined bauxitic kaolin
clay with water and a dispersant in a high shear Cowles dissolver
to achieve a slurry having the reported solids content. The clay
had an alumina content of about 50 weight percent alumina, and was
obtained from JF Blecher. The dispersant used was a sodium
polyacrylate commercially available under the tradename C-211 from
Kemira Chemicals, and was used in the amount reported in Table 3,
which is a percent by weight of the dry clay used to make the
slurry. Polyvinyl alcohol (PVA) having a molecular weight of 25,000
Mn was added to Sample Nos. 4 and 5 in an amount of about 0.30
percent by weight of the dry clay used to make the slurry. The PVA
can be obtained from DuPont under the tradename Elvanol.
[0059] The slurry solids content reported in Table 3 was determined
using a Ohaus MB45 moisture balance at 190.degree. C. until all
physical moisture was eliminated. The viscosity data was determined
using a Brookfield RVF viscometer with a number 1 spindle @ 20 rpm,
which is commercially available from Brookfield Engineering
Laboratories, Middleboro, Mass. The Brookfield viscometer was
operated according to the procedures provided for its
operation.
[0060] The slurries were atomized according to the atomization
conditions reported in Table 3. Each slurry was fed to a dual fluid
nozzle atomizer at ambient temperature, at the feed rate, and under
the atomization pressure, reported in Table 3. The duration
reported in Table 3 indicates the time that the slurry was pumped
at the indicated rate in order to make droplets of the slurry.
[0061] The same nozzle design was used for each Sample reported in
Table 3. The nozzle type was an Air Atomizing Nozzle 1/4J,
commercially available from Spraying Systems, Inc. The nozzle was
configured with a flat spray, external mix, spray set up no. SUE
45, and pressure set up, according to Spraying Systems Catalog 60B
Express (2000), which is a text available to those of ordinary
skill in the art for operation of Spraying Systems nozzles. The
nozzle was configured in a Drytec Nozzle Tower pilot unit, which
had a drying chamber of 1.000 meters in diameter and 2.000 meters
in cylindrical height with an overall spray height of 2.866
meters.
[0062] As the atomized droplets of slurry exited the pressure
nozzle, they were exposed to the Drying Conditions reported in
Table 3. Hot air was fed to the drying chamber at the reported
rate, which was measured using the pressure drop across the cyclone
vessel. The reported inlet and outlet temperatures of the drying
chamber were determined with type K thermocouples.
[0063] As moisture evaporated from the droplets due to contact with
the hot air feed, green ceramic particles were formed having the
Green Properties reported in Table 3. The reported residual
volatiles % was determined with a CSC moisture analyzer based on
complete moisture loss on drying, and indicates moisture that did
not evaporate from the particle during drying. The poured density
represents that amount of green particles that filled a container
of known volume, while the tapped density represents that amount of
green particles that filled a container of known volume with
tapping of the container as it was filled.
[0064] The green particles were sintered in a static, Blue M
Lindberg lab kiln to produce substantially round and spherical
solid ceramic particles. Sintering was achieved using a heating
rate of 12.degree. C./min to a peak temperature of 1510.degree. C.
with a 30 minute hold at peak temperature. Sintered Properties of
the sintered solid ceramic particles such as size, grain fineness
number, bulk density, apparent specific gravity and crush strength
are reported below.
[0065] The bulk density, apparent specific gravity and crush
strength were determined using API Recommended Practices RP60 for
testing proppants.
TABLE-US-00003 TABLE 3 Sample No. 1 2 3 4 5 6 7 Slurry Properties:
Solids (wt %) 64.6 64.6 64.6 59.9 59.9 68.2 50.0 Dispersant (wt %)
0.075 0.075 0.075 0.075 0.075 0.15 0.15 PVA (wt %) 0 0 0 0.30 0.30
0 0 Density (g/cc) n/a n/a n/a n/a n/a n/a n/a Viscosity at 20 RPM
282 282 282 430 430 334 n/a (centipoises) Atomization Conditions
Feed Rate of slurry 3.5 3.5 3.5 3.5 3.5 3.5 3.2 (gal/hr)
Atomization Pressure 80 80 70 70 60 60 60 (psig) Duration (min.) 11
19 18 18 57 25 43 Drying Conditions: Drying Air Rate 6.08 6.08 6.08
7.25 7.25 4.35 8.35 (kg/hr) Inlet Air Temp. .degree. C. 274 274 274
274 274 274 274 Outlet Air Temp. .degree. C. 104 93 99 104 119 119
119 Green Properties: Residual Volatiles, % 3.8 4.6 4.4 1.0 0.6 8.3
0.6 Poured Density, g/cc 1.20 1.20 0.85 0.81 0.79 0.97 0.76 Tapped
Density, g/cc 1.25 1.25 0.90 0.86 0.84 1.01 0.80 Particle Size,
microns 90% less than 14.17 47.82 16.92 17.63 16.69 97.81 5.92 50%
less than 3.13 3.51 2.82 3.16 3.74 5.21 1.64 10% less than 0.84
0.78 0.78 0.83 0.90 1.00 1.42 Product Wt. (kg) 1.248 2.187 2.061
1.087 3.458 3.958 1.144 % Retained on Sieve U.S. Mesh No. (or pan)
30 0.4 0.9 2.1 0.0 0.0 5.7 0.1 40 1.3 4.2 4.5 0.2 0.1 15.1 0.1 50
5.2 8.1 9.8 0.9 0.8 21.3 0.2 70 12.4 12.8 13.7 3.0 4.0 25.7 0.3 100
18.4 17.4 17.1 7.4 10.5 18.1 0.7 140 19.4 17.4 17.1 7.4 10.5 18.1
0.7 200 14.9 13.5 13.1 16.0 16.9 3.3 9.6 270 14.7 12.5 11.4 19.8
20.4 1.3 32.6 pan 13.3 13.2 10.8 39.8 33.5 0.6 53.4 Avg. Size,
microns 144 167 183 80 88 306 51 (including pan material) Sintered
Properties (30/270 material was sintered) Sieve, U.S. Mesh 30 0.0
0.0 0.0 0.0 0.0 0.0 0.0 40 0.5 0.2 2.1 0.1 0.1 1.3 0.4 50 1.6 2.2
5.6 0.5 0.6 12.6 0.7 70 6.1 9.2 10.8 2.5 3.8 18.5 1.0 100 17.5 21.5
22.0 13.8 16.3 35.4 2.8 140 26.3 26.9 24.7 25.4 23.8 20.2 7.4 200
18.8 17.8 15.8 22.9 21.2 6.9 12.6 270 18.1 14.3 11.9 21.3 21.0 4.0
24.4 pan 11.1 7.9 7.1 13.5 13.2 1.1 50.7 Avg. Size, microns 121 133
154 104 109 199 62 (including pan material) Grain Fineness 118
109.7 101.5 128.6 125.6 78.7 155.6 Number (GFN) (does not include
pan material) Bulk Density (g/cc) 1.47 1.44 1.45 1.28 1.26 1.58
1.22 Apparent Specific 2.77 2.83 2.84 2.81 2.74 2.81 2.81 Gravity
(ASG) Crush on -50/+140: 7500 psi % Crush 10.0 15.9 15.4 47.3 44.1
5.2 n/a
[0066] The exemplary slurries described in Table 3 illustrate that
slurries having a solids content of greater than about 50 weight
percent, greater than about 60 weight percent, and greater than
about 65 weight percent can be maintained at viscosities suitable
for feeding through atomizing equipment of a spray dryer. The
solids content of the slurries contributed to the formation of
solid, substantially round and spherical particles as described
herein.
[0067] The bulk densities and ASGs reported in Table 3 indicate
that at least some of the sintered particles were solid. The low
inlet air temperatures (which are determined by lower outlet air
temperatures) used to process the slurries of this Example 3
contributed to the production of solid particles. Moreover, binder
was not used to make the solid, substantially round and spherical
particles described in Table 3.
[0068] In addition, the largest average particle sized material was
produced from the highest residual volatile sample (Sample No. 6).
The residual volatile content of Sample No. 6 indicates that Sample
No. 6 was exposed to a reduced drying rate as compared to those
samples discharged from the drying chamber with lower residual
volatile contents. Thus, a reduced drying rate should contribute to
the production of ceramic particles having properties as described
herein.
[0069] Further still, the values reported in Table 3 show that
particles having a size, a bulk density, an apparent specific
gravity and a 7500 psi crush strength suitable for use as propping
material may be produced using slurries prepared as described
herein, and processed with spray dryer technology.
EXAMPLE 4
[0070] Referring now to Table 4 below, the results of seven test
runs that produced substantially round and spherical solid ceramic
particles according to the methods disclosed herein are reported.
Values reported in Table 4 as "n/a" were not determined.
[0071] The particles were produced from about a 5 gallon batch of
slurry that was prepared by agitating a calcined bauxitic kaolin
clay with water and a dispersant in a high shear Cowles dissolver
to achieve a slurry having a solids content of about 59.5 weight
percent, a viscosity at ambient temperature, 60 RPM, of about 130
centipoises, a pH of about 9.5 (by addition of ammonium hydroxide),
and contained about 0.03 wt. percent of a dispersant, based on the
weight of the dry clay starting material.
[0072] The dispersant was a sodium polyacrylate produced by Kemira
Chemicals under the tradename C-211. The clay had an alumina
content on a calcined basis of about 47 weight percent, and was
obtained as calcined material, (calcined to about 2 wt. % loss on
ignition), from CE Minerals, Andersonville Ga.
[0073] The slurry was not immediately processed through the spray
dryer, and therefore the viscosity had to be modified with
additional dispersant to bring the viscosity back to a value such
that the slurry could be sprayed. As the first run of slurry was
processed, an additional 7.1 grams of the C-211 brand dispersant
was added. After the first run, an additional 7.2 grams of the
C-211 brand dispersant was added, such that the total amount added
to the slurry as batched was 14.3 grams. No additional dispersant
was added after the second run, thus, the total amount of
additional dispersant remained 14.3 grams, as reported in Table
4.
[0074] When sprayed to form particles, the slurries had a solids
content and viscosity as reported in Table 4. The slurry solids
content reported in Table 4 was determined using an Ohaus MB45
moisture balance at 190.degree. C. until all physical moisture was
eliminated. The viscosity data was determined using a Brookfield
RVF viscometer with a number 1 spindle @ 20 rpm, which is
commercially available from Brookfield Engineering Laboratories,
Middleboro, Mass. The Brookfield viscometer was operated according
to the procedures provided for its operation.
[0075] The slurries were atomized according to the atomization
conditions reported in Table 4. Each slurry was fed to a dual fluid
nozzle atomizer at ambient temperature, at feed rates and under
atomization pressures as reported in Table 4. The duration reported
in Table 4 indicates the time that the slurry was pumped at the
indicated rate in order to make droplets of the slurry.
[0076] The same nozzle design was used for each Sample reported in
Table 4. The nozzle type was an Air Atomizing Nozzle 1/4J,
commercially available from Spraying Systems, Inc. The nozzle was
configured with a flat spray, external mix, spray set up no. SUE
45, and pressure set up, according to Spraying Systems Catalog 60B
Express (2000), which is a text available to those of ordinary
skill in the art for operation of Spraying Systems nozzles. The
nozzle was configured in a Drytec Nozzle Tower pilot unit, which
had a drying chamber of 1.000 meters in diameter and 2.000 meters
in cylindrical height with an overall spray height of 2.866
meters.
[0077] As the atomized droplets of slurry exited the pressure
nozzle, they were exposed to the Drying Conditions reported in
Table 4. Hot air was fed to the drying chamber at the reported
rate, which was measured using the pressure drop across the cyclone
vessel. The reported inlet and outlet temperatures of the drying
chamber were determined with type K thermocouples.
[0078] As moisture evaporated from the droplets due to contact with
the hot air feed, green ceramic particles were formed having the
Green Properties reported in Table 4. The reported residual
volatiles % was determined with a CSC moisture analyzer based on
complete moisture loss on drying, and indicates moisture that did
not evaporate from the particle during drying. The poured density
represents that amount of green particles that filled a container
of known volume, while the tapped density represents that amount of
green particles that filled a container of known volume with
tapping of the container as it was filled.
[0079] The green particles were sintered in a static, Blue M
Lindberg lab kiln to produce substantially round and spherical
solid ceramic particles. Sintering was achieved using a heating
rate of 12.degree. C./min to a peak temperature of 1510.degree. C.
with a 30 minute hold at peak temperature. Sintered Properties of
the sintered solid ceramic particles such as size, grain fineness
number, bulk density, apparent specific gravity and crush strength
are reported below.
[0080] The bulk density, apparent specific gravity and crush
strength were determined using API Recommended Practices RP60 for
testing proppants.
TABLE-US-00004 TABLE 4 Sample No. 1 2 3 4 5 6 7 Slurry Properties:
Solids (wt %) 56.2 56.2 56.2 56.2 56.2 56.2 56.2 Dispersant (wt %
as 0.03 0.03 0.03 0.03 0.03 0.03 0.03 batched) Additional
Dispersant 7.1 14.3 14.3 14.3 14.3 14.3 14.3 (grams, as sprayed)
Viscosity at 20 RPM 385 385 385 385 385 385 385 (centipoises)
Atomization Conditions Feed Rate of slurry 2.0 2.0 2.0 2.0 2.0 3.0
4.0 (gal/hr) Atomization Pressure 80 80 80 60 45 45 45 (psig)
Duration (min.) 30 30 35 10 30 15 15 Drying Conditions: Drying Air
Rate N/A N/A N/A N/A N/A N/A N/A Inlet Air Temp. .degree. C. 227
256 221 219 227 297 313 Outlet Air Temp. .degree. C. 118 118 107
107 107 107 107 Green Properties: Residual Volatiles, % 3.2 3.7 1.1
3.6 2.9 7.3 11.5 Poured Density, g/cc N/A 0.62 0.59 0.63 0.64 0.84
1.42 Tapped Density, g/cc N/A 0.65 0.61 0.66 0.70 0.87 1.45
Particle Size, microns 90% less than N/A 7.54 403.93 9.72 54.15
33.55 40.54 50% less than N/A 2.26 4.32 3.33 41.02 3.64 8.84 10%
less than N/A 0.76 0.90 0.89 1.69 0.84 1.42 Product Wt. (kg) 0.227
0.488 0.989 0.417 1.783 1.075 2.155 % Retained on Sieve U.S. Mesh
No. (or pan) 30 N/A 0.1 0.0 0.1 0.0 0.1 0.1 40 N/A 0.1 0.1 0.1 0.2
0.8 1.8 50 N/A 0.7 0.6 0.5 1.9 4.4 7.8 70 N/A 3.9 3.2 2.6 6.2 9.6
12.7 100 N/A 8.4 6.4 5.7 12.2 14.3 16.0 140 N/A 16.2 12.6 12.2 19.6
17.9 17.8 200 N/A 20.6 18.6 21.6 27.0 17.5 16.7 270 N/A 30.5 32.7
32.7 22.6 19.9 17.2 pan N/A 19.1 24.7 24.6 9.7 15.4 10.0 Avg. Size,
microns N/A 92.8 82.7 82.6 112.6 126.9 150.9 (including pan
material) Sintered Properties (30/270 material was sintered) Sieve,
U.S. Mesh 30 N/A 0.5 0.2 0.0 0.0 0.1 0.2 40 N/A 1.3 0.1 0.1 0.1 0.2
0.7 50 N/A 2.5 0.3 0.4 1.7 3.4 1.7 70 N/A 3.2 2.0 3.0 5.9 9.4 2.5
100 N/A 5.1 4.8 8.0 10.5 13.4 5.3 140 N/A 8.7 7.9 13.4 16.1 17.8
10.5 200 N/A 11.8 11.4 15.8 17.3 16.9 14.9 270 N/A 17.6 16.6 19.6
18.9 17.1 21.2 pan N/A 49.2 56.7 39.7 29.6 21.6 43.1 Avg. Size
(microns) N/A 82.7 62.9 79.0 96.9 117.4 79.0 (includes pan
material) Grain Fineness N/A 132.3 142.1 135.9 126.5 116.4 139.7
Number (GFN) (does not include pan material) GFN with pan N/A 214.9
231.7 201.0 177.8 156.1 208.8 Bulk Density (g/cc) N/A 1.38 1.21
1.25 1.41 1.42 1.38 Apparent Specific N/A 2.75 2.62 2.66 2.78 2.78
2.78 Gravity (ASG)
[0081] The exemplary slurries described in Table 4 illustrate that
slurries having a solids content of greater than about 50 weight
percent can be achieved at viscosities suitable for feeding through
atomizing equipment of a spray dryer. The solids content of the
slurries contributed to the formation of solid, substantially round
and spherical particles as described herein.
[0082] The bulk densities and ASGs reported in Table 4 indicate
that at least some of the sintered particles were solid. The low
inlet air temperatures (which are determined by lower outlet air
temperatures) used to process the slurries of this Example 4
contributed to the production of solid particles. Moreover, binder
was not used to make the solid, substantially round and spherical
particles described in Table 4.
[0083] In addition, the largest average particle sized material was
produced from the highest residual volatile sample (Sample No. 7).
The residual volatile content of Sample No. 7 indicates that Sample
No. 7 was exposed to a reduced drying rate as compared to those
samples discharged from the drying chamber with lower residual
volatile contents. Thus, a reduced drying rate should contribute to
the production of ceramic particles having properties as described
herein.
EXAMPLE 5
[0084] From the methods developed through Examples 1-4, it is
possible to estimate the dimensions of spray drying equipment, in
particular, the drying chamber, that could produce particles larger
still than those actually produced in Examples 1-4.
[0085] Referring now to FIG. 4, an estimate of desirable equipment
dimensions is illustrated. The heights of the drying chambers of
Examples 2 and 3, and the volume of the green particles produced
therein are plotted on FIG. 4 at points 1 and 2, respectively.
Point 3 on FIG. 4 corresponds to the height (about 9.8 m) of a
production spray drying chamber manufactured by, and available for
testing at, American Custom Drying. Assuming a linear relationship
established by points 1 and 2, a drying chamber having a 9.8 m
height should produce a green pellet volume of about 0.110
mm.sup.3. Continuing the assumption of a linear relationship,
points 4 and 5 plotted on FIG. 4 correspond to a desired green
pellet volume of about 0.212 mm.sup.3 and 0.234, respectively.
Given such desired green pellet volume, the estimated height of the
drying chamber the estimated height of a drying chamber for making
such volumes were estimated and completed the plotting of points 4
and 5.
[0086] As illustrated in FIG. 4, the estimated height of a drying
chamber for making 30/50 proppant sized pellets (approximately an
average green pellet size of 765 microns) would be 19.8 meters.
Utilizing industrial screening machines such as Rotex Inc Model
522, the dried pellets may be screened, providing proppant pellets
sized to yield 20/40, 20/30, or 18/40 products.
[0087] A drying chamber having a height of 19.8 meters as described
herein could have a diameter of about 7.4250 meters and a volume of
about 857.33 m.sup.3. Those of ordinary skill in the art would
recognize that the dimensions of the drying chamber described in
this Example 5 can vary, and that other diameters and ratios can be
designed.
[0088] Selection of dimensions of for the drying chamber, in
combination with the methods already discussed herein, namely,
maximizing the solids content of the slurry, minimizing the amounts
of solubles (e.g., dispersants and/or binders) in the slurry) while
still maintaining a sprayable viscosity, lowering the inlet and
outlet air temperatures fed to the drying chamber, should produce
substantially round and spherical solid ceramic particles, that,
when sintered, have an average particle size, bulk density,
apparent specific gravity and crush strength suitable for use as
proppant material.
[0089] According to the present methods, solid spherical ceramic
particles are produced by adjusting one or more of (I) solids
content (preferably higher solids content in the slurry); (2)
solubles content (preferably minimal or no dispersant and/or binder
in the slurry); and (3) air inlet temperatures (preferably a low
temperature to slow the drying rate of the particles). In addition,
controlling the drying air flow rates through the drying chamber
(preferably a low rate), can contribute to the production of solid
spherical ceramic particles as described herein. Moreover,
selection of equipment dimensions, such as the height of the drying
chamber of the spray dryer, can enhance the average size of the
particles produced according to methods described herein.
[0090] The substantially round and spherical solid ceramic
particles that are produced according to the methods described
herein are suitable for a variety of uses, including but not
limited to use as a proppant in oil or gas wells, and as a foundry
media. Other embodiments of the current invention will be apparent
to those skilled in the art from a consideration of this
specification or practice of the invention disclosed herein.
However, the foregoing specification is considered merely exemplary
of the current invention with the true scope and spirit of the
invention being indicated by the following claims.
* * * * *