Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background of the Invention
This invention relates to granular sorptive
carriers, and more particularly to methods for producing
granular sorptive carriers using calcium sulfate hemi-
hydrate. The sorptive carrier granules produced ac-
cording to this invention are substantially neutral and
are useful as inert carriers for chemicals and particu-
larly for agricultural chemicals.
A number of solid materials are widely used as
carriers for agricultural chemicals, such as insecticides,
herbicides, fertilizers, and the like. The agricultural
chemicals are combined with such a carrier for convenient
dissemination by various distributor means.
In some types of agricultural carriers, the
chemical or active ingredient contained therein is in
solid form, usually as a powder or as small particles or
granules, and is admixed with the carrier, the mixture
then being formed into pellets. With other types of
carriers, the carrier is in the form of particles or
granules into which the active ingredient, in liquid form,
is sorbed. With yet another type of carrier the active
ingredient is adhered to the carrier surface.
Agricultural carrier material can be used in
many forms, such as powder, particles, granules, or pel-
lets. For ease of handling, and for other reasons, mate-
rials having a granule size in a range which would pass
through a 20-mesh screen and be retained on a 60 mesh
screen (U.S.A. Standard Sieve Series) are commonly used.
With such size granules, it is important that the gran-
ules maintain their structural integrity and thus sizeduring initial fabrication as well as during subsequent
storage, marketing, and application. In many applica-
tions, it is important that the particles or granules be
of a size that does not pass through the 60-mesh screen
so as to reduce the probability that some of the particles
or granules are so small as to form dust. It is also
important that the particles maintain their size and con-
dition so that they do not form dust, or turn to dust,
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owing to degradation during storage or use, or owing to
general abrasion or attrition during manufacturing,
handling, storing, transporting and application with
mechanical devices to agricultural soil. Dust is ob-
jectionable because of the well known problems with dustspreading in the air and on persons and animals, and
being inhaled by workers making or handling such carriers.
Many naturally-occurring mineral carriers that
are used with agriculturally active ingredients, includ-
ing certain types of pesticides, have a degree of surfaceacidity which varies depending upon the crystalline and
molecular structure of the mineral. It is thought that
the surface acidity arises as a result of a non-uniform
distribution of electric charge in or on the surface or
the mineral particles. A large number of electric charges
may exist at certain areas on a surface of a mineral car-
rier particle and these are referred to as acid sites or
electrophilic centers. The strength of these centers
varies depending upon the composition of the surface and
the degree of distortion in the structure which brings
about the non-uniform distribution of the electrical
surface charges. The surface acidity on a mineral car-
rier particle can affect the reactivity of that mineral
particle with the agricultural chemical carried thereon.
It is thought that the surface acidity, and specifically
the acid centers, have a catalytic effect with respect
to the decomposition of the particular chemical. It has
been found that with some pesticidal chemicals, the
catalytic ac~ivity of the acid sites, with respect to
inducing or accelerating decomposition, can be much re-
duced by deactivation of the acid sites with certain
organic or inorganic materials which preferentially share
their electrons with the mineral to form a bond which is
stronger than that which may be formed between the agri-
cultural chemical and the acid center itself. The addi-
tion of any deactivator material, usually in amounts of
up to 6 or 8 percent by weight of the carrier adds an
~z~6~;8.
undesirable cost to the formulation of the agricultural
chemical-laden carrier. Thus, it would be desirable to
provide a method for producing a substantially neutral
and inert carrier for agricultural chemicals, and es-
pecially for pesticides, which has little or no surfaceacidity and which does not require the addition of any
deactivator material.
A sorbent carrier for liquid chemicals should
have a relatively high sorptivity, or a sorptivity which
is at least high enough to prove commercially satisfac-
tory.
In the case of sorbent materials, the porosity
of the material is usually related to the sorbency char-
acteristics of the material. Further, a generally low
dry bulk density is usually a characteristic of the more
sorbent materials. Generally, as particle or granule
size increases, the bulk surface area decreases for a
given number of granules. Since sorptivity is princi-
pally a surface phenomenon and a function of the pore
density within a surface, it would be desirable to pro-
, vide a method for producing a carrier granule having a
size small enough to present a relatively high bulk sur-
face area and having a pore density high enough such
that the sorp~ivity is commercially satisfactory.
In order that a granulated carrier functions
properly and does not degrade through abrasion or attri-
tion into dust under mechanical stress during manufacture,
packaging, storing, shipping and use, the carrier granules
must exhibit adequate mechanical strength. Thus, it would
be desirable to provide a method for producing a carrier
granule which has relatively high mechanical strength or
resistance to attrition while minimizing the concurrent
generation of an undesirable amount of small, dust-size
particles.
The present invention provides a very effecti~e
method for controlled manufacture of relatively low-
density, gypsum-containing granules that are eminently
1~2~ 8
suitable as carriers for agricultural chemicals and -that are
resistant to attrition. Additionally, the low-density, gypsum-
containing granules produced according to the method of this
invention are also useful as oil and grease sorbents, as sorbents
for household pet toilets, and for similar applications.
_ mmary of the Invention
According to the method of the present invention, a
particulate charge containing calcium sulfate hemihydrate
(CaSO4.1/2H20) is treated with an aqueous binder in an amount
sufficient to wet and agglomerate the particles of the charge,
and to initiate hydration of the calcium sulfate hemihydrate
present while being subjected to vigorous mechanical action. The
charge particles and aqueous binder are fed into a confined
elongated space in which a generally helical turbulent gas stream
is generated. The charge and aqueous binder orm a substantially
uniform dispersion of the particles within the turbulent gas
stream which dispersion is subjected to mechanical agitation so
as to pack the wetted particles into granules. Thereafter the
granules are recovered from the gas stream.
Thus, in accordance with the present invention, there is
provided a method for producing sorbent calcium sulfate dihydrate-
containing granules which comprises: providing a particulate
charge comprising finely divided calcium sulfate hemihydrate
particles having a size that passes through a 60 mesh screen,
said charge containing calcium sulfate hemihydrate in an amount
of at least about 35 percent by weight of the charge; providing a
confined elongated space and generating a generally helical
turbulent gas stream within said space; feeding said charge into
said gas stream so as to provide a substantially uniform disper-
sion of said particles in said gas stream, the space time for the
particulate cnarge within the turbulent gas stream being about
1.4 x 10 4 hours to about 1 x 10 3 hours; introducing into said
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~; ~
~LZ916~3
dispersion an aqueous binder in an amount sufficient to wet and
agglomerate said particles, and to initiate hydration of said
calcium sulfate hemihydrate while in said dispersion; mechanically
agitating said dispersion such that the flow of said dispersion
is substantially the same as that of said gas stream so as to
pack the wetted particles into granules; and recovering the
granules thereby produced.
The present invention may also be defined as a method for
producing sorbent calcium sulfate dihydrate-containing granules
which comprises: providing a particulate charge comprising sor-
bent particles having a size that passes through a 60 mesh screen
and at least about 35 percent by weight of the charge of plaster
of Paris particles mixed therewith mechanically agitating a gas
within a confined, elongated space so as to produce a generally
helically shaped turbulent gas stream therein; feeding said charge
into the produced gas stream at a substantially uniform rate so
that the space time for the particulate charge within the
turbulent gas stream being about 1.4 x 10 hours to about 1 x 10 3
hours; feeding an a~ueous binder into the produced gas stream sub-
stantially simultaneously with said charge in an amount sufficientto wet the particulate charge and to initiate hydration of said
plaster of Paris particles; continuing said agitation for a time
period sufficient to form granules; and recovering the produced
granules.
The granules produced in accordance with this method have
a relatively high mechanical strength or resistance to attrition
-to mechanical stresses during manufacture, packaging, storing,
shipping and other uses. Additionally, the sorbent carriers made
in accordance with this invention are relatively inert and have
sorptivities which are high enough for commercial use as sorbent
materials. Still another advantage of -the method of this in-
vention is that the particle size distribution of the produced
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668
granules can be controlled within a relatively narrow range.Yet another benefit of the method of this invention is that
the sorptive granules produced have a bulk density which is
lower than that of naturally occurring gypsum particles and,
as discussed hereinabove, provide higher sorptive capacity
than naturally occurring
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IL2~8
gypsum particles of similar size. Numerous other advan-
tages and features of the present invention will become
readily apparent from the following detailed description
of the invention, the accompanying examples, and from the
appended claims.
Descri tion of the Preferred Embodiments
P
While the method of this invention is suscept-
ible of embodiment in many different forms, specific
embodiments will be herein described in detail, with the
understanding that the present disclosure is to be con-
sidered as an exemplification of the principles of the
invention and is not intended to limit the invention to
the embodiments illustrated.
All references made herein to sieve analysis,
screen mesh sizes, particle sizes, and the like are ex-
pressed using the designations of U.S.~. Standard Sieve
Series-ASTM Specification E-11-70.
In accordance with the method of this invention,
sorbent calcium sulfate dihydrate (CaSO4 2H2O) or gypsum-
containing ~ranules are produced by first providing aparticulate charge comprising finely divided calcium sul-
fate hemihydrate (CaSO4 1/2H2O) particles with or without
other particulate absorbent material being present. This
charge contains at least about 35 percent by weight cal-
cium sulfate hemihydrate, commercial grades of which arealso known as plaster of Paris. Preferably, the particu-
late charge contains at least about 50 percent by weight
plaster of Paris.
In order for the granulation process of this
invention to be most successful, substantially all of the
particles in the charge r and particularly the plaster of
Paris particles, should be wet with an aqueous binder as
will be discussed in greater detail hereinbelow. Conse-
quently, the charge particles should be of a small enough
diameter such that they may be so wet. It has therefore
been found beneficial to use charge particles whose sizes
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are such that they will pass through a 60-mesh screen.
More preferably, and beneficially, the charge particles,
and therefore plaster o~ Paris particles, should be of a
size such that the particles will pass through a 325-mesh
screen.
The charge may also be comprised of other sor-
bent particles, i.e., supplemental sorbent materials, in
addition to the plaster of Paris particles. These other
sorbent particles may be selected from an extremely wide
range of organic as well as inorganic materials. As is
the case of the plaster of Paris, preferably substantially
all particles of the other sorbent materials present in
the charge should be wetted by the aqueous binder during
the granulation process. It is also beneficial to have
the particle size of the other sorbent materials similar
to that of the plaster of Paris, i.e., particles having a
size such that they will pass through a 60-mesh screen,
and most preferably particles of sizes which will pass
through a 325-mesh screen.
Particularly useful such other sorbent particles
or supplemental sorbent materials include inorganic mate-
rials such as absorbent clay minerals, vermiculite,
diatomaceous earth, pumice~ Portland cement, gypsum,
activated carbon, and the like. Particulate botanical
materials such as ground corn cobs, oat mill feed, soybean
mill feed, alfalfa meal, coconut meal, ground cottonseed
hulls, ground rice hulls, chopped hay, wood flour, and the
like are also useful for the present purposes.
Particulate absorbent clay minerals are particu-
larly preferred. These materials are natural, earthy pro-
ducts composed primarily o~ hydrous aluminum silicates.
Small amounts of non-clay materials may also be present.
Typical absorbent clay minerals are montmorillonite, kaolin,
illite, halloysite, vermiculite, the sodium and calcium
bentonites (clays largely composed of montmorillonite but
may contain beidellite, attapulgite, and similar minerals),
attapulgite, sepiolite, and the like. Calcium bentonite
is a particularly preferred clay mineral for the present
purposes. Calcium bentonite can range in color from a
cream, off-white, to a dark reddish tan color and is fre-
quently referred to in the trade under designations such
as Mississippi brown, Georgia brown and Georgia white
clays.
Gypsum containing particles such as those made
in accordance with this invention but whose sizes are such
that they are either too large to be commercially useful
and therefore have been crushed for reuse, or those whose
sizes are too small for commercial use can also be simply
added back into the charge of a subsequent preparation of
sorbent granules.
Additionally, the particulate charge may also
contain coloring materials, should variously colored
granules be desired, and also agents which may retard or
hasten the hydration reaction and therefore the setting
into a solid state of the plaster. Retarding agents are
usually of a colloidal nature such as glue, sawdust,
blood, packing-house tankage, and the like. Hastening
agents are frequently crystallized salts such as sodium
chloride, sodium sulfate, sodium carbonate, and the like.
The granules of this invention are produced in
a reactor having a confined, elongated space which often
may be tubular. Within this space a ~enerally helical
turbulent gas stream is generated, e.g., by rotating im-
pellers, vanes, or similar means, and the particulate
charge is introduced therein. The introduced particulate
charge is suspended in the turbulent gas stream, is sub- --
jected to mechanical agitation within the confined space,
wetted by the aqueous binder, and follows a generally
helical path which is substantially the same as that of
the turbulent gas stream. The preferred gas is ambient
air. However, heated or cooled air may be employed as
well as other gases such as nitrogen, carbon dioxide,
argon and the like.
66~3
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For optimum agitation of the suspended particu-
late charge along its path in the reaetor, the mechanical
agitation is induced by a series of impellers whieh are
spaced along the length of the reactor. Each of the im-
pellers preferably is eomprised of a plurality of bladesor paddles which impinge on the suspended particulate
charge and on the wet granules as they are formed. In
preferred reactors, the angle o~ the blades or paddles may
be changed as desired to thereby control the degree of
physical agitation produced by each impeller as well as
the residence time of the suspended particulate charge
within the reactor.
A reactor which has been found useful for prac-
ticing the present invention is commercially available
from the Strong-Scott Mfg. Co. of Minneapolis, Minnesota,
under the trade name TURBULIZER. A TURBULIZER is de-
seribed by its manufaeturer as a "h;igh speed eontinuous
mixer," and a suggested use for it is the de-agglomeration
and homogenizakion of solids. However, it has now been
found that this machine, when operated in a certain manner
can also be used to make granules from very small parti-
cles, or fines. The designation of a Strong-Scott TURBULI-
ZER as a reaetor in which the method of this invention can
be aceomplished, is for illustrative purposes only, sinee
the method of this invention is not limited to using only
this particular reactor brand or reactor design.
In earrying out the method of this invention, as
the reactor's meehanical agitation is begun, a turbulent
helical gas flow is generated within the reactor by the
rotating reactor paddles or vanes therein. As a partieu-
late charge is fed into the reactor, the particles consti-
tuting the charge enter the gas stream and create therein
a substantially uniform dispersion of the charge particles.
An aqueous binder is also introduced into the reactor in
an amount sufficient to wet the charge particles and ini-
tiate hydration of the calcium sulfate hemihydrate while
i6~
the particles are in the dispersion created within the
reactor. Thus, a new dispersion containing gas, water,
supplemental sorbent particles (if present),and hydrating
calcium sulfate hemihydrate is produced. Within the reac-
tor, the aqueous binder preferably wets substantially allof the charge particles and in so wetting causes the cal-
cium sulfate hemihydrate to begin its conversion to the
dihydrate. The calcium sulfate hemihydrate, as it is in
the process of hydrating, under the influence of the
mechanical agitation that takes place within the reactor
along the aforementioned helical gas flow agglomerates
with the various other materials present within the reac-
tor to form substantially spherical absorbent granules.
The aqueous binder used in this method is prefer-
ably water as it is received from the tap. Distilled ordeionized water may also be used. ~dditionally, additives
may be included into the water such as polymeric materials
which aid the granulation process and also add some mechan-
ical strength to the granular product of this invention.
Examples of polymeric materials which may be used in the
water include but are not limited to polyvinyl alcohol
containing resins, soluble acrylic resins as well as water
insoluble but dispersible acrylics as are used in forming
paints and the like.
It is preferred that the particulate charge and
aqueous binder are fed into the reactor and gas stream
substantially simultaneously, thus, a fore-run of the
particulate charge does not emerge from the reactor prior
to the desired product nor does the aqueous binder emerge
prior to the granulated product.
The amount of aqueous binder used is a function
of its water content, and the amount of calcium sulfate
hemihydrate tplaster of Paris) present in the charge. The
amount of water used should be near the stoichiometric
amount required to convert the calcium sulfate hemihydrate
to calcium sulfate dihydrate, i.e., plaster of Paris, to
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gypsum. Preferably, the amount of water used is in slight
excess over that which would be required by the stoichio-
metry of the hydration reaction. At the stoichiometric
point, about 6 weights of plaster of Paris would consume
about 1 weight of water. Most preferably, water should
not be used at more than about 25 percent of the weight
of the plaster, or said in a different fashion, the most
preferable weight ratio between plaster of Paris and water
fed to the reactor at any given time is about 4 weights of
plaster of Paris to one weight of water.
Granules prepared in accordance with the prefer-
red amounts of water emerge from the reactor slightly damp,
but as the hydration reaction is allowed to continue, the
granules dry by themselves. It is assumed that the water
which causes the dampness either evaporates into the sur-
roundings, or more likely, it is used to continue hydration
of the plaster into gypsum. If substantially more water is
used than that within the preferred range, the mechanical
strength of the granules may suffer. Also, the granules
leaving the reactor must be dried, which requirement adds
another step and therefoxe increases the cost of produc-
tion.
As the reactor hereinabove described is one which
does not allow a significant amount of backmixing, the
aqueous binder should be fed into the reactor in a quantity
which is sufficient to hydrate that portion of the particu-
late charge which is also being fed. Thus, it is preferred
that the aqueous binder be fed into the reactor and its gas
stream at a rate such that the weight of aqueous binder fed
is no greater than about 25 percent by weight of the charge
which is simultaneously being fed.
The manner in which the aqueous binder is fed
into the reactor may vary. Thus, if water alone is used
as the binder, it may be fed in the form of steam or water
vapor. Additionally, an aqueous binder may be fed as a
liquid stream to be broken up by the mechanical agitators.
~2~
Preferably, it is fed as a liquid in particulate form,
i.e., as a spray or fog. Several different types of ori-
fices are known in the art for spraying aqueous solutions
or dispersions and particular choices of these orifices or
nozzles are left to be chosen by those skilled in the art
depending upon the particular type of granule desired, the
particle size of the charge being fed, the binder being
used, and the particular requirements of the reactor which
is chosen.
The size of the produced granules is dependent
to a large extent on the processing time of the particu-
late charge within the reactor. In general, the longer
the processing time the larger will be the average size,
i.e., diameter of the produced granules. However, for any
given reactor, the time elapsed in processing one reactor
volume of dispersed particulate charge to be granulated at
steady state conditions, the space time, should be at
least 0.5 seconds to allow for wetting of the plaster of
Paris particles and formed granule compaction by mechanical
agitation.
Space time, ~,can be calculated by dividing the
reactor volume by the volumetric flow rate of reactor
output. The reciprocal of space time ~, is space velocity,
S, i.e., 5 = l/~.
As an example, using a granulation reactor having
a reactor volume of about 3.35 cubic feet, such as Turbuli-
zer Model T-l~, granules predominantly in the 20/60 mesh
size, i.e., passing through a 20-mesh screen and retained
on a 60-mesh screen, can be produced at a rate of about
2500 pounds/hour while feeding through the reactor about
2000 pounds/hour of commercial grade plaster of Paris and
about 500 pounds/hour of water as a finely divided spray
together with ambient air as carrier gas at a rate of about
270 cubic feet per minute or about 16,200 cubic feet/hour.
Accordingly, the approximate space time for the foregoing
granulation process is about 2 x 10-4 hours.
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In general, it has been found that a space time
of about 1.4 x 10-4 hours to about 1 x 10-3 hours is pre-
ferable in producing granules by the method of this inven-
tion such that at least about 20 weight percent of the
granules will pass through a 20-mesh screen and be re-
tained on a 60-mesh screen. Space times of aboutl.8 x 10-4
hours to about 2.2 x 10-4 hours are preferred for produc-
ing granules whose sizes are such that at least about 85
weight percent of the granules will pass through a 20-mesh
screen and be retained on a 60-mesh screen.
The granules produced by the method of this in-
vention generally have a dry bulk density of about ~0
pounds per cubic foot and less, depending on the constitu-
ents that are present, and preferably of about 40 to about
lS 55 pounds per cubic foot. These granules generally have a
surface hardness of less than about 40 percent attrition
and a liquid holding capacity of at least about 30 percent
by weight.
The fact that the surface hardness of the gran-
ules of this invention is less than about 40 percentattrition is an indication that the granule of the pre
sent invention is particularly well suited for commercial
use as a carrier for liquid chemicals, and especially as
a carrier for agricultural chemicals, which are sorbed in
or on the granule and which can be deposited upon agricul-
tural sites by spreading the granules on such sites using
ordinary agricultural implements. Specifically, the rela-
tively high surface hardness imparts a degree of mechanical
strength or resistance to attrition under the mechanical
stresses encountered during the formulation process, during
packaging, and shipping, as well as during use wh~n the
granules are spread by mechanical apparatus on agricultural
sites.
The relatively high surface hardness further con-
tributes to a relatively low dustability characteristic ofthe granule. That is, the granule o the present invention,
~3L2~68
having a relatively high surface hardness, has a lesser
tendency to break down and form small dust particles or
"fines" which are generally undesirable because the fines
spread through the air and are transported to areas where
they are not wanted and also because they may be inhaled
by animals and/or workers handling the granules.
The calcium sulfate dihydrate granules of the
present invention provide granules which are substantially
inert with respect to the agricultural chemicals for which
they are intended to serve as a carrier. It is believed
that this carrier material has few, if any, catalytic
sites or acid sites, which tend to cause or accelerate
decomposition of various chemicals abs~rbed on the gran-
ules. Thus, the use of deactivator compounds i5 not
ordinarily required with this granule to neutralize acid
centers as is required with many other types of carriers.
It is to be noted that the calcium sulfate dihy-
drate granule of the present invention has a bulk density
of less than about 55 pounds per cubic foot when prepared
in accordance with the method of the present invention to
be described hereinafter. This compares favorably with the
bulk density of naturally occurring gypsum (calcium sulfate
dihydrate) of between 65 and 70 pounds per cubic foot.
Though this reduction in bulk density cannot be currently
satisfactorily explained, such a reduction in bulk density
is highly desirable because it is some indication of the
sorptivity capability. The oil holding capacity of the
granules of the present invention is at least about 30 per-
cent by weight, and may reach 100 percent depending on the
granule constituents. The water holding capacity of these
granules is about the same, to slightly higher than the oil
holding capacity.
The preferred size of the granule of the present
invention falls within a range wherein the granule will
pass through a 20-mesh screen and be retained on a 60-mesh
screen. This size granule has dry flow characteristics and
66~
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handling characteristics that make it eminently suitable
for use as a carrier of agricultural chemicals.
The presence of fines in the charge affects the
surface hardness of the ultimately produced absorkent
granule, thus the surface hardness can also be regulated
by controlling the amount of fines present in the parti-
culate charge to the reactor. In general, the particulate
charge can contain up to about 50 percent by weight fines.
The higher the concentration of these fines in the charge
the lower will be the surface hardness of the ultimately
produced granules.
A number of examples will be presented herein-
after for the purposes of further illustrating and dis-
closing the present invention. These examples are by way
of illustration, and are not to be taken as limiting.
With each example, there $s provided a tabula-
tion of parameters relating to the initial charge of mate-
rial, the process conditions, and the characteristics of
the final product. Certain terms or properties that have
been used or referred to in the pre~3ent specification,
including the following examples, axe defined or deter-
mined as follows:
1) "Bulk Density" is the measured loose packed
density of the agglomerated product when dried to no more
than 1 wt.-~ free moisture. A 250 ml. graduated cylinder
is completely filled with the product without tamping.
The bulk density in pounds per cubic foot is determined
by dividing the weight of the sample in grams by the
volume of the sample in milliliters and multiplying by
the factor 62.43.
2) "Water Absorption" is determined by the fol~
lowing procedure. First, a sample of about 50 grams from
the dried product is weighed to the nearest 0.1 gm. and
poured into a glass tube measuring 9 inches in length and
30 mm. in internal diameter. The glass tube is maintained
in a vertical position and one end of the tube is covered
with a Number 18-mesh screen. Fine particles passing
-15-
through the screen are collected and returned to the top
of the tube. The glass tube is held on a tripod stand and
positioned at a 30 angle to the horizontal. A 100 ml.
graduated cylinder is placed under the tube at the screen.
75 ml. of water is introduced from a pipette
through the open end of the 9-inch-long glass tube to the
sample. The water is absorbed by the sample until the
saturation point is reached and the surplus water begins
draining into the graduated glass cylinder. This step is
continued until all portions of the sample in the tube are
wet. After insuring that no part of the sample in the '
tube is dry, the tube is allowed to drain for 30 minutes.
Next, since 75 ml. of water was initially present in the
; pipette, and since any water not absorbed by the sample in
the tube is collected in the graduated cylinder below the
tube, the amount of water absorbed is equal to the initial
75 milliliter quantity minus the volume of water collected
in the graduated cylinder. This amount is divided by the
weight of the sample in grams to provide the absorption
capacity of the sample in units of ml./gm.
3) "Oil Absorption`' was determined in accordance
with the test specified in Bulletin P-A-1056, Federal Spec-
ification/ Absorbent Material, Oil and Water (For Floors
and Decks), issued by the General Services Administration
of the United States of America. The observed absorption
capacity is reported in units of ml./gm.
4) "Surface Hardness" is reported as percent
aitrition and is determined as follows: A nest of two
standard testing sieves, sieve No. 8 and sieve No. 60, each
having a circular shape and an eight-inch diameter are
selected for use with a Ro-Tap mechanical sieve machine
manufactured by W. S. Tyler Co. of Dayton, Ohio. An ali-
quot of 100 grams, weighed to the nearest 0.1 gm., is with-
drawn as a sample from the granulated product. The sample
is placed on the No. g sieve in the sieving machine for 5
minutes of shaking. The material passing through both the
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No. 8 sieve and the No. 60 sieve and ending up in the col-
lecting pan beneath the No. 60 sieve is rejected along with
any larger material unable to pass through the No. 8 sieve.
50 grams of material retained on the No. 60 sieve is
placed in a pan along with 300 grams of 1/4-inch diameter
steel balls and hand mixed. The pan is then shaken in the
mechanical sieving machine for 20 minutes without the
tapping arm engaged. The contents of the pan are placed
on the top, No. 8, sieve and allowed to fall through to the
No. 60 sieve and retaining pan below the No. 60 sieve. The
steel balls are removed from the No. 8 sieve and the ma-
chine is mechanically sieved for 5 minutes with the tapping
arm engaged. The material that is passed through the No.
60 sieve is then weighed. The hardness, in terms of "break
down percent" or attrition is calculated by dividing the
weight of the material that has passed through the No. 60
sieve by 50 grams and multiplying by 100.
5) "Liquid Holding Capacity". In testing liquid
holding capacity (dry flow), a low viscosity organic liquid
having a specific gravity of 1 gm./ml. is used. A one to
one mixture (by weight) of Heavy Aromatic Naphtha and ortho
chloro toluene will give the desired specific gravity and
viscosity, and be relatively non-volatile. The procedure
is as follows: -
(A) Place 20 grams of granules in an 8 ounce
French square bottle.
(B) Add 5-gram increments of liquid to the gran-
ules and for each increment sha~e the bottle (a) until no
granules cling to the sides or (b) for 5 minutes.
(C) When sufficient liquid has been added that
granules still cling to the sides of the glass after 5
minutes of shaking, add l-gram increments of dry granules
(with a 5 minute shaking interval for each addition until
the point is reached where no granules cling to the sides
of the container). At this point the liquid holding capa-
city (L.H.C.) is calculated as follows:
~z~
-17-
cc (or grams) of liquid
% L.H.C. = - X 100
grams of granules + grams of liquid
6) The "Screening Distribution Analysis" pre-
sented in each example summarizes the results of a standard
test to determine the distribution of granule sizes in the
product charge. At the end of the granulation process, the
batch of produced granules was dried. Thereafter, five
standard circular, 8-inch diameter sieves or mesh screens
were used in the analysis and were placed in nested, de-
scending order with respect to screen size (mesh opening).Approximately 200 grams of the granule product was placed
on the top sieve, and the sieves were shaken for five min-
utes using a Ro-Tap mechanical sieve machine. The weight
retained on each tared sieve was converted to percent
retention of the 200-gram sample and is listed in the tab-
ulation for each example under the sieve or mesh number on
which it is retained. A listing of a pair of sieve or
mesh numbers separated by a virgule t/) indicates that the
granules had passed through the first number sieve or
screen and had been retained on the second number sieve or
screen. A sieve or mesh number preceded by a plus (+) sign
indicates that the granules were retained on the sieve or
screen, whereas a sieve or mesh number preceded by a minus
(-) sign indicates that the granules passed through the
sieve or screen.
EXAMPLE 1
A model T-l~ Strong-Scott TURBULI~ER reactor was
used to granulate commercial grade plaster of Paris. About
1900 pounds of plaster of Paris per hour were fed to the
reactor together with a water spray at a rate of about 25
percent by weight of the plaster of Paris feed rate. The
produced gypsum granules were then recovered and dried.
About 2200 pounds of gypsum granules per hour were obtained
having a bulk density of about 57 pounds per cubic foot and
the following screen analysis:
6~i8
-18-
Screen ~ by Weight
-
+ 4 0.3
+ 6 1.3
+ 8 2.6
+ 10 2.1
+ 12 4.3
-~ 16 15.0
+ 20 23.9
+ 60 40.4
- 60 10.1
100.0
EXAMPLE 2
A Model T-14 Strong-Scott TURBULIZER reactor was
used to granulate a mixture of about 50 weight percent
Canadian plaster and about 50 weight percent Mississippi
brown clay having a particle size passing through a 60-
mesh screen. Prior to granulation the particulate mate-
rials were pre-blended in a cement mixer having a~out four
cubic eet capacity.
; 20 Turbulizer Operating Conditions
Feed Rate: 1850 ~/hr
Water Feed Rate: 1.5 gal/min
Output: 2600 #/hr, wet
2000 #/hr, dry
Shaft Speed: 728 rpm
Paddle Setting: 45o
Power Draw: 20 amps, with surges
to 60 amps, at240 volts
Wet granules were recovered from the reactor and dried as
a fluidized bed under the following conditions:
Inlet Temperature: 90C.
Final Outlet Temperature: 40C
Batch Size: 75 # wet
Time Required per Batch: 25-30 min
Damper Settings: 100% Inlet
100% Outlet
~2~1668
--19--
The dried granules were then subjected to a size reduction
operation.
Crusher and Screen Operating Conditions
Throughput: 800-1000 #/hr
Number of Passes: 4 to 5
Before size reduction:
Yield, Wt.-%
Screen Batch #1 Batch #2 Batch #3
+ 20 55 S0 37
20/60 33 37 34
- 60 12 13 29
100 100 100
After 1st pass at crushing the + 20 from Batch ~3:
Screen Yield, Wt.-%
+ 2072
20/60 12
- 60 16
100
After 2nd pass using + 20 from 1st ;pass:
Screen Yield, Wt.-%
+ 2083
20/60 9 ,~
- 60 8
100
After 3rd pass using ~ 20 from 2nd pass:
Screen Yield, Wt.-%
+ 2051
20/60 31
- 60 18 .~.
100
Overall yield on Batch #3:
Screen Yield, Wt.-%
~ 20
20/60 55
- 60 45
100
31 ~Z~6~
-20-
Product Evaluation
Bulk Density:
Loose 44.0 #/ft.3
Packed 47.8 #/ft.3
O'Haus 41 #/ft.3
Absorption:
Oil 0.9 ml/gm
Water 0.8 ml/gm
Hardness 25.3%
Free Moisture 1.1%
Bound Moisture 11.4%
pH 7.2
Color grey
pKa 1.5 negative
3.3 positive
Screen Analysis
Screen Wt.-%
o
~ 30 17.2
+ 40 34.1
50 41.1
6.1
- 60 1.5
EXAMPLE 3
The same reactor as in Example 2, above, was used
to granulate a mixture of about 60 weight percent Canadian
plaster and about 40 weight percent Mississippi brown clay
having a particle size passing through a 60-mesh screen.
The foregoing mixture was prepared by blending the afore-
mentioned materials in a cement mixer having about four
cubic feet capacity.
Turbulizer Operating Conditions
Feed Rate: 18g0 #/hr
Water Feed Rate: 1.63 gal/min
Output: 2700 #/hr, wet
2070 #/hr, dry
~i2~66B
-21-
Shaft Speed: 728 rpm
Paddle Setting: 45O
Power Draw:20 amps,withsurges to
60 amps, at 240 volts
The wet granulated output from the reactor was recovered
and dried as a fluidized bed under the following conditions:
Inlet Temperature: 90C.
Final Outlet Temperature: 40C.
Batch Size: 75 # wet
T.ime required per Batch: 20-25 min
Damper Settings: 100% Inlet
100% Outlet
The obtained dry granules were then subjected to size re-
duction.
Crusher and Screen Operating Condit:ions
Throughput 800-1000 #~hr
Number of passes 4 to 5
Before size reduction:
Yield, Wt.-%
_ _
Screen Batch #1 Batch #.2 Batch #3
+ 20 54 45 51
20/60 31 31 38
- 60 15 24 11
25100 100 100
After crushing + 20:
_
Yield, Wt.-%
Screen Batch #1 Batch #2 Batch #3
30+ 20 0 0 0
20/60 68 64 62
60 32 36 38
100 100 100
Overall yield of 20/60:
Weighted
Batch #1 Batch #2 Batch #3 Average
68~ 60% 70% 68%
i68
-22-
Product Evaluation
.
Bulk Density:
Loose 44.9 #/ft.3
Packed 49.8 #/ft.3
O'Haus 44 #/ft.3
Absorption:
Oil 0.8 ml/gm
Water 0.8 ml/gm
Hardness 25.5
Free Moisture 1.1
Bound Moisture 11.0
pH 7.1
Color grey
pKa 1.5 negative
3.3 positive
Screen Analysis
Screen Wt.-%
+ 20 0
~ 30 19.6
+ 40 35.9
~ 50 37.2
+ 60 5.5
- 60 1.8
; The foregoing specification and data are intended
as illustrative of the present invention and are not to be
taken as limiting. Variations in processing parameters
within the spirit and scope of the invention disclosed
hereinabove are possible and will readily present them-
selves to one skilled in the art.
- 30
