Note: Descriptions are shown in the official language in which they were submitted.
1~85776
APPARATUS AND METHOD FOR PNEUMATICALLY SEPARATING
PRACTIONS OF A PARTICULATE MATERIAL
This apparatus relates generally to particle separation and more
particularly to the separation of particulate material through the usé of
upwardly moving streams of air or other gas.
The classification of particulate material according to density
and/or aerodynamic properties by passing the particulate mixture through
zones of differing air velocity has been known and practiced for a number of
years. Air classification systems have been used for removing rocks or
other foreign matter from such commodities as wheat, tea, raisins, wood
chips and the like. A primary separation of light from heavy materials is
an exceedingly important first step in the handling of heterogeneous parti-
culate material. Because of the increasing cost of energy and raw materials ~
the efficiency of this first separation step may be critical in determining ,
the overall cost efficiency of a materials handling system.
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Recently, compliance with environmental restrictions
has necessitated the recycling of municipal garbage and in-
dustrial waste which in many cases are collected without dis-
crimination and contain a diverse mixture of heavy materials
such as glass, metal and stones, and of lightweight materials
such as paper, leaves and plastic. It is advantageous to
separate lightweight from heavyweight materials since in most
instances, the lightweight material is combustible and thus
usable as a source of energy if separated from the heavier
materials.
A variety of different apparatuses have been pro-
posed to perform particle separation. The efficiency of these
prior art separators has been limited by eatures which were
heretofore considered necessary for a succes~ful separation
process. Some of these apparatuses include complex duct arrange-
ments to create turbulences in the material-bearing gas stream
and thereby to improve material separation. Such designs are
expensive to con~truct. Also, because of the high turbulence
they create, a relatively great amount of energy is invested
in moving a gas column through the tortuous ducts.
In other devices a stream of air moves upward in an
essentially uninterrupted, straight column. A plurality of
outlets on one side of the column are provided for materials
to fall through according to their density. If, however,
materials of any density or aerodynamic property migra~e to
the outlets of such a device, they fall through the outlets.
The efficiency of separation is low because particles of low
density and low aerodynamic characteristics will be carried
out through outlets provided for the collection of denser or
more aerodynamic particles.
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In still other apparatuses heterogeneous material is carried into
a series of columns having upwardly moving gas in each column. Because each
column in the series contains gas moving upward at a velocity lower than that
of the preceding column, only those particles having the desired density or
aerodynamic properties can fall through to the base of each column. Although
the accuracy of separation in such devices is good, the operating costs have
been relatively high since they have included numerous fans to be driven and
many zones of high turbulence where particulate material and/or gas must
reverse direction.
Summary of the Invention ;;
It has now been discovered that a highly efficient separation of
heavy and light particles may be conducted at a relatively low energy con- -
sumption by feeding the heterogeneous material into columns of air which move
continuously upward in substantially vertical ducts.
The invention provides apparatus for pneumatically separating frac-
tions of a heterogeneous mixture of particulate material according to relative
densities and/or aerodynamic properties comprising: an unobstructed, sub-
stantially straight primary duct which is not inclined from vertical by more
than about ten degrees and which narrows near the top to define a region of
accelerating airflow; airlock feed means for feeding material to be separated
into said primary duct at a location upstream of said region of accelerating
airflow and without admitting a substantial amount of air into said primary
duct; a discharge duct connecting with the top of said primary duct and
extending upwardly therefrom; means for producing an upwardly moving column
of air in said primary and discharge ducts having a velocity operable to
raise a light fraction of said material while a heavy fraction falls to the -
bottom of said primary duct; a secondary duct which is displaced horizontally
from said primary duct and which communicates with only said discharge duct
and the surrounding atmosphere so that said secondary duct provides an inlet
for admitting a column of air directly, entirely from the surrounding atmos-
phere into the interior of said discharge duct at a location shortly down-
` stream of said region of accelerating airflo~, to increase the volume of air
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in said upwardly moving column of air in said discharge duct; and adjustable
damper means operable to ad~ustably constrict said secondary duct for
regulating the velocity of air moving through said discharge duct.
Particulate material is fed into a first upward moving column of
air having a velocity such that a buoyant fraction of the material is raised
in the column and a dense fraction falls through the column. The first
column of air is deflected toward and merged into a second upward moving
column of air displaced horizontally from the first column. The combined
column is caused to move upwardly at a velocity less than the velocity in
the first column so that heavier particles of the buoyant fraction and any
dense particles which may have been unintentionally carried into the combined
column will fall down into the second column and then fall to the base of that
column. Lighter materials of the buoyant fraction are carried off by the
combined column to a remote point. For maximum flexibility, the apparatus
for this operation is designed such that the velocity of air in each column
may be ad~usted independently.
Brief Description of the Drawings
In the drawings:
Figure 1 is a sectional side elevation of the material separator;
and
Figure 2 is a schematic diagram showing the material separator of
Figure 1 incorporated as a part of a complete material separation system.
Description of the Preferred Embodiment
Referring to Figure 1, the preferred embodiment of the separator
of the present invention has a generally vertical duct structure which
includes a primary sorting duct 12, the base of
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which defines an output port 14. Opening into the primary
duct 12 near the top is a material input duct 16. The primary
sorting duct 12 may be substantially vertical as shown by
solid lines or may be inclined at an angle ~ under the input
duct 16 as shown by broken lines. Preferably the angle ~ is
not more than ten degrees from vertical and more preferably not
more than five degrees. Conveniently, means are provided for
introducing particulate material into the input duct 16 without
allowing air to enter the duct. While such means may take a
variety of forms, one suitable form is a rotary star feeder 18 as
shown in Fig. 1.
A secondary sorting duct 24 is positioned adjacent to
the primary sorting duct 12. The width of the secondary sorting
duct is reduced near it~ top to form a venturi 34. Because the -
throat of this venturi is the narrowest portion of the secondary
sorting duct, the column of air moving through the secondary
sorting duct reaches maximum velocity as it passes through the
venturi 34. This area of high velocity serves as a barrier to
low density particles which might fall into the venturi 34. The
gecondary sorting duct 24 is provided at its bottom with an
output port for the removal of particulate material and could,
optionally, be fitted with suitable discharge apparatus such
as a rotary star discharge apparatus. An air inlet is provided
to admit air into the secondary sorting duct 24. In the embodi~
ment of Figs. 1 and 2 and orifice 26 is provided which serves
as both the output port and the air inlet. Alternatively, the
secondary sorting duct 24 could include an air inlet and a
separate output port such as an airlock discharge device. In
either case a damper means may be provided to regulate the
flow of air through the inlet. One suitable damper means is
the damper 32 shown in Fig. 1.
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Both the pri~ary sorting duct 12 and the secondary
sorting duct 24 open into the bottom of a discharge duct 20.
An airfoil 22 is provided at the junction of the material
input duct 16 and the discharge duct 20 to reduce the turbulence
of air flowing up through the primary sorting duct 12 and into
the discharge duct 20. In the preferred embodiment, the duct
work includes a region 23 of reduced cross-sectional area near
the top of the primary sorting duct so that the airflow and
particulate material at that point are accelerated into the
discharge duct 20. The discharge duct 20 includes a lower por-
tion immediately above the sorting ducts 12, 24 which is sized
so that the velocity of air moving through such lower portion
is less than the velocity of air moving through the primary
sorting duct 12. Because the velocity of air in the lower por-
tion of the discharge duct 20 is reduced, the densest particles
in the discharge duct can fall downwardly into the venturi 34
and thus be collect~d in the secondary sorting duct 24. The
lower portion of the discharge duct 20 iq inclined over the
secondary sorting duct 24 at a small angle o from vertical so
that an outer wall 36 of the discharge duct serves as a steep
ramp which empties into a funnel-shaped mouth 37 of the venturi
34. Preferably the angle o is about five to fifteen degrees .
from vertical. It is desirable, but not essential, that the
discharge duct 20 narrow in its upper regions, as illustrated
in Fig. 1, so that the column of air bearing the lighter par-
ticles of the buoyant fraction accelerates upwardly when it
enters the narrowed region.
In the illustrated embodim~nt, the side walls of the .:
various ducts are movable so that the cross-sectional area of
the ducts and thus the velocity of air flowing through the
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ducts may be adjusted. A plurality of hinges ~8 may be pro- '' ' "
vided for ease in moving the side walls. An adjustable means
of support, such as turnbuckles 40 hold the walls in the de-
sired po~ition.
Means are also provided for producing upward moving '
columns of air in each of the various ducts. The columns are
preferably produced by a single suction means adapted to cause
a negative pressure in the discharge duct 20. In this preferred
configuration the output port 14 and orifice 26 are open to the
surrounding atmosphere. Alternatively, upward moving columns
of air in the various ducts may be provided by blowers which
move columns of air upward through the primary and secondary ',
sorting ducts 12, 24,at elevated pressures or by any other suit-
able means for creating upward moving columns of air in those
ducts.
Operation
In operation, a heterogeneous mixture of particulate
material is fed into the material input duct 16 by the rotary
~tar feeder 18. The material falls by gravity into the primary ,
sorting duct 12 where it encounter~ a first upward moving column
of air. A dense residual fraction of the material continues to
fall by gravity through the primary sorting duct 12 and eventually
through the output port 14. A conveyor, bin or other suitable
means (not shown) may be provided beneath the output port 14
for collecting the residual fraction. The downward acceleration
due to gravity of a buoyant fraction of the material is overcome
by the upwardly moving column of air. This buoyant fraction is ,-
raised by the column to the point 23 and from there accelerated
into the discharge duct 20.
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The column of air carrying the buoyant fraction and
a second column of a7r, moving upwardly in the secondary sort-
ing duct, merge as they enter the lower portion of the discharge
duct 20. Because the cross-sectional area of the lower portion
of the discharge duct 20 is large by comparison to the combined :
cross-sectional areas of the duct at the point 23 and the venturi
34, the merged column of air moves through the discharge duct 20 :
at a lower velocity than the column of air moving through the
duct at the point 23. In order to collect particulate material
10 in the secondary sorting duct it is necessary that the cross-
sectional areas of the discharge duct be set such that air moves
through lower portion of that duct at a velocity not greater than
the velocity of air in the primary sorting duct 12.
In this zone of decreased velocity, heavier particles
of the buoyant fraction can no longer be supported by the moving
column of air and will fall downwardly. Some of the heavier
particles of the buoyant fraction fall against the outer wall
36 and, because the air flow will be ~lower there, may there-
after roll or slide down into the mouth 37 of the venturi 34.
20 Other of the heavier particles fall directly into the funnel
shaped mouth 37. Any of the heavier particles which fall
back toward the point 23 are again raised on the high velocity
column of air which enters the discharge duct 20 from the pri- ~ .
mary sorting duct 12. Because the discharge duct 20 is in-
clined, the high velocity column of air carries most of
these heavier particles to a position from which they can
fall against the wall 3~ or directly into the mouth 37. All
of the particles which fall into the mouth 37 encounter a
second column of air which flows upwardly through the venturi
30 34. The particles continue to fall to the bottom of the second-
ary sorting duct 24 only if the downward gravitational forcs
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acting on the particles is sufficient to overcome the upward
force of this second column of air. Those particles which
succeed in falling to the bottom of the secondary sorting duct
24 are thereafter discharged through the output port formed
5 by the orifice 26. Those lighter particles of the buoyant
fraction which are not accelerated downwardly by gravity when
they enter the discharge duct 20 are instead carried up into
the upper regions of the discharge duct 20 and thereafter
through an upper output port 42.
The density and/or aerodynamic characteristics of
particles which enter the secondary sorting duct 24 may be
regulated by the damper 32 which is adjustable to vary the
flow of air through the throat of venturi 34. In order for
material to fall into the secondary sorting duct, it is neces-
15 sary that the damper be adjusted so that the velocity of air
moving upwardly through the venturi 34 is not substantially
greater than the velocity of air moving in the primary sort-
ing duct. If it is desired that the secondary sorting duct
be used to collect a fraction of particulate material of a
20 lesser average density than the material collected in the
primary sorting duct 12, the velocity of air moving through
the venturi 34 is adjusted to be less than the velocity of
air in the primary duct. To prevent lightweight particles
from falling into the secondary sorting duct 24, the velocity
25 of air moving through the venturi 34 is adjusted to be not
substantially less than the velocity of air moving through
the lower portion of the discharge duct 20.
As previously described, the air velocities in the
primary sorting duct 12 and the discharge duct 20 may be varied
30 by moving the side walls of those ducts. In the preferred
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embodiment of the invention the walls of those ducts are posi-
tioned so that the desired velocity ratios are achieved by
adjusting the damper 32 t~ admit, through the secondary sorting
duct, about ten to twenty percent of the total amount of air -
moving through the entire system.
The present invention has been successfully used for
the separation of rocks from wood chips. In this application,
rhe materials to l~e separated are essentially of two densities
only. For this reason the velocity of air in each column is
adjusted to maximize the collection of rocks in both the pri-
mary and secondary sorting ducts so that wood chips carried
out of the discharge duct on the combined columns of air are
substantially free of rocks. Tests using the improved materials
separator of the present invention demonstrated a highly ef-
ficient removal of 0.25 inch diameter rocks from wood chips.
The separator used for these tests had a primary sorting duct
174 sq. in. in cross-sectional area, a discharge duct with a
lower portion 234 sq. in. in cross-sectional area, and a venturi
having a cross-sectional area of twentv-four sq. in. In each
20 run, the discharge duct was inclined at five degrees from ;~
vertical and air moved through the venturi at a velocity of
twenty to thirty feet per second. The results of several
typical runs are listed in Table I.
TABLE I
Primary sort- Air velocity Rocks Discharged (percent)
ing duct in primary Primary~-S-econdary T~
Run No. inclination sorting duct sorting sorting
(ft/sec.) duct duct _
1 0 48.9 90.3 3.7 94.0
2 0 49.3 88.2 7.3 95.5
3 5 53.3 96.2 1.9 98.1
4 10 53.0 88.1 6.0 94.1
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The separator of the present invention is also well
suited for the primary separation of shredded municipal waste.
When used for this purpose, the various ducts are preferably
adjusted so that the columns of air in both the sorting ducts
and the discharge duct move upward at a velocity sufficient to
raise lightweight materials such as paper and plastic which
are generally combustible, but insufficient to raise heavier
materials. At these conditions, the only particles which are
collected in the secondary sorting duct 24 are those particles
of the dense residual fraction which instead of falling through
the bottom of the primary sorting duct 12, are unintentionally
accelerated into the bottom of discharge duct 20. As compared
to single column separators of similar capacity, the capture
of material in the secondary sorting duct 20 of the present
invention accounts for an overall improvement in separation of
approximately five to ten percent.
Fig. 2 illustrates the ~eparation apparatus of the
present invention in a complete system for processing shredded
waste. Except for the material separator of the pre~ent inven-
tion, all of the equipment illustrated is of standard design.
Shredded refuse is fed into the rotary airlock feeddevice 18 of the present invention. The residual fraction of
material discharged from a separation apparatus at the output
port 14 of the primary sorting duct and/or the heavier particles
of the buoyant fraction which are discharged from the orifice
26 of the secondary sorting duct are collected by any suitable
means. ~he lighter particles in the buoyant fraction are
carried upwardly through the discharge duct 20 into a cyclone
60 which serves as a convenient separating means where the
lightweight particulate materials are separated from the column
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of air. Other conventional devices for separating solid
particles from a gas would serve equally well for the same
purpose. The lightw~ight particles are discharged from the
bottom of the cyclone via a suitable airlock discharge device
62 and thereafter collected and transported to any desired
location. If the air moving through the system is contaminated
by toxic gases or lightweight solids, such as dust or lint,
which might be harmful to the environment, a suitable treatment
apparatus, indicated at 66, may be installed in the system to
scrub undesirable contaminànts from the air. A blower 68 is
the sole means for moving air through this preferred system.
It draws air through the entire system by creating a negative
pressure in the duct indicated at 70. Air passing through
this system is discharged to the atmosphere from the outlet 72 ;;
of the blower. To achieve maximum flexibility and efficiency,
the blower 68 should be adjustable to vary the flow of air
through the system and be equipped with automatic controls to
maintain the flow of air at a constant rate so that particles
collected in the various ducts of the separation apparatus will
be within a uniform range of densities.
The separating apparatus of the present invention
may also be used in a closed cystem. In a closed system,
environmental discharge are further reduced and/or gases other
than air may be used to transport the particulate material.
The complete system described above may be modified to a sub-
stantially closed system by returning gas from the outlet of
the blower to the output port 14 and orifice 26 which serves
as gas inlets of the sorting ducts.
~ hile I have shown and described a preferred embodi-
ment of my invention, it will be apparent to those skilled in
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the art that changes and modifications may be made without
departing from my invention in its broader aspects. I there-
fore intend the appended claims to cover all such changes and
modifications as fall within the true spirit and scope of my
invention.
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