Note: Descriptions are shown in the official language in which they were submitted.
WO 96/09901 ~ 3 Q PCT/US95/12095
PATENT APPLICATION
IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
TIT~F~
LOW VELOCITY AIR DENSITY SEPARATOR
FIELD OF THF INVFNTION
The present invention relates to apparatuses and methods for
separating fractions of a partic~ te material in general. More particularly, thepresent invention relates to apparatuses and methods for utilizing air to
separate components of a particulate material on the basis of differing
attributes.
BACKGROUND OF THF INVFNTION
The separation of a particulate material into various fractions on the
basis of density is performed in many industrial processes. In the mining
industry, heavy minerals are concentrated from ores for extraction. In
agriculture, grain is separated from chaff and leaves are separated from stalks
by the use of a current of air which lifts the lighter chaff or leaves away from the
grain or stalks. In the wood pulping industry, a device known as an air density
separator has been employed to separate wood chips of light colored wood
from chips containing knots which are more dense.
The air density separator uses a vertical separdlion chamber through
which a stream of air is drawn with a velocity in the range of four to five
thousand feet per minute. Wood chips to be separated are metered by an
auger into the separation chamber where the high velocity air stream disperses
the chips evenly over the chamber. The more dense knots fall through the
uprising current of air and are rejected. The lighter chips are drawn from the
separation chamber by the flow of air and separated from the air by a cyclone.
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WO 96/09901 PCT/U~95/12095
Recent concern with waste reuse and progress in recycling
post-consumer wastes have given rise to new and unique problems in the
separation of materials. Voluntary, and in some cases mandatory, recycling
has resulted in the collection and separation of a number of specific
post-consumer packaging materials which have been identified as being
constructed of a high volume ",dlerial and thus likely candidates for economic
recycling. Materials which have been so identified are the ubiquitous aluminum
cans, glass bottles, plastic milk cartons and 1, 2 and 3 liter pop bottles.
The recycling of milk bottles and pop bottles has been identified as a
candidate for economic recovery. However, the value of the recycled product
is heavily dependent on its purity.
The recovery of high value materials from post-consumer wastes plays
a critical role in reducing the landfill disposal of post-consumer wastes. High
value products such as aluminum cans, newspapers, and plastic can reduce
the cost of governmental subsidies and help finance the recovery of otl1er
rl~dlerials from the waste stream. Further, the production of and marketing of
the most valuable components of municipal waste creales a market and social
cli,lldle for recycled products which is key to the economic recovery of a larger
and larger fraction of consumer wastes. One major problem in recycling
post-consumer plastic bottles is the removal of the labels, typically paper, from
the plastic bottles.
What is needed is an apparatus and method for removing paper and
thin gauge plastic from post-consumer plastic bottles.
SUMMARY OF THE INVFNTION
The air density separation apparatus of the present invention employs a
vertical air separation chamber. The vertical air separation chamber is
WO96/09901 22~ 13 39 PCI/US95112095
connected to a cyclone which in turn is connected to a fan. The fan draws air
out of the cyclone which in turn causes air to be drawn up through the
open-bollo~"ed separation chamber. In prior art air density separators utilized
in separating wood chips from wood knots, air is drawn rapidly up through the
separation cha"ll~ar at four to five thousand feet per minute. The wood chips
are metered into the separation chamber through an air lock or a supply auger.
The auger dumps the chips into the high velocity air sl~ea", where the high
velocity air disperses the chips across the separation chamber so that the
rising stream of air may separate the chips based on their density and
cross-sectional area.
With the low velocity air density separator of this invention, the
separation chamber is somewhat longer and the air is drawn up through the
chamber at approximately seven hundred to eight hundred feet per minute.
Because of the relatively low velocity of the air, the air stream itself is
noneffective at dispersing the shredded plastic bottles and their associ~ted
paper labels evenly into the air stream. In order to achieve the even
distribution of the shredded bottles and the labels into the air sl,ean" a grid of
closely spaced narrow bars extends into the separation chamber. The bars are
cantilevered into the separation chamber and are c~llsed to vibrate by an
oscillatory mounting. The shredded material may be fed by an ordinary chute
without an air lock onto the deck of the grid of bars. Air moving rapidly
between the bars lifts and sepaldles the various co"~liluents of the shredded
bottles. The denser plastic walls of the bottle fall down through the bars and
are recovered as the heavy recyclable fraction of the bottles. The lightweight
paper is drawn up through the separation chamber and into the cyclone. The
cyclone removes the lightweight paper from the air stream and air is drawn
from the cyclone by a fan. In tests with material of a bulk density of 18.5
pounds per cubic foot, the air density separator of this invention is estimated to
WO 96/09901 2 2 0 1 ~ 3 Q PCT~USg5/12095
remove ninety-five to ninety-eight percent of the paper from a feed of shredded
plastic bottles with a loss of plastic with the paper of only zero to one percent.
It is a feature of the present invention to separate shredded paper from
shredded plastic.
It is another feature of the present invention to purify recycled plastic
from post-consumer waste.
It is a further feature of the present invention to provide an air density
separation apparatus for separating sand, dirt and wood dust from wood chips.
It is a still further feature of the present invention to provide a method
wherein post-consumer plastic waste may be purified for recycling.
It is a yet further feature of the present invention to provide an
apparatus for feeding and distributing a granular material into an air stream.
Further objects, features and advantages of the invention will be
apparent from the following detailed desc, i~.lion when taken in conjunction with
the acco"~panying drawings.
BRIFF DFSCRIPTION OF THF DRAWINGS
FIG. 1 is a side-elevational somewhat schematic view of the low velocity
air density separator of this invention.
FIG. 2 is an isometric view, partly cut away, of the separation chamber
and infeed mechanism of the low velocity air density separator of FIG. 1.
~ WO 96/09901 2 ~ ~ ~ 3 3 9 PCT/US95/12095
DFSCRIPTION OF THE pF~FFFRFaFn EMBODIMF~IT
Referring more particularly to FIGS. 1-2 wherein like numbers refer to
similar parts, a low velocity air density separator 20 is shown in FIG. 1.
The air density separator 20 has a vertically disposed conduit 22 which
defines a vertical air separation chamber 24. Mixed particul~te matter 44 is
introduced into the separation chamber 24 from a material hopper 58. The air
separation chamber 24 is connected by a duct 26 to a cyclone 28. The
cyclone is connected to a fan 30. The fan draws air from the cyclone 28 which
in turn draws air through the duct 26 which causes a ~l~eam of air indicated by
arrows 32 to enter the bottom 34 of the conduit 22.
The mixed material 44 is discharged from the hopper 58 along an
inclined chute 60 onto a foraminous screen formed by a grill 36 disposed within
the separation chamber 24. The grill 36 has a multiplicity of closely spaced
narrow bars 38 which extend across the conduit 22 between a material inlet 40
and a trash outlet 42. The grill 36 is cantilevered from a mount 46 which
resiliently supports the grill 36 on springs 48. A fenu,nagnetic member 50 is
mounted to the grill 36 and is driven by a solenoid 52 to cause the grill 36 to
vibrate at about sixty Hertz. Certain mdl~lial will be entrained in the upwardlymoving air and will leave the separation chamber through the duct 26. The
remaining particul~te material which is not entrained and which is of a size to
pass through the grill 36 will exit the separation chamber 24 through the bottom34 of the conduit 22 and will be collected on a conveyor 35.
In a conventional air density separator, air is drawn up through the
separation chamber at four to five thousand feet per minute while the granular
material to be separated such as wood chips is dispensed into the air chamber
either by a chute with an air lock or by an auger which distributes the materialacross the separation chamber. In a conventional air density separator the
=
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WO 96/09901 PCTIUS9S/12095
high velocity air stream moving up through the separation chamber is effective
to disperse the granular material being separated in the air stream. Materials
which are suffciently dense fall down through the separation chamber whereas
lighter materials become entrained in the air and are drawn into a cyclone
where they are separated.
An air density separator separates a particulate matter depending
on what is known in the aerodynamic field as ballistic coerricient. R~llistic
coefficient is a function of the density of the object, the area of the object
presented to the air stream, and a shape-dependent coefficient. Thus, the
ballistic coeffcient of an object increases with its density, decreases wi~:h
increasing area and decreases with increasing bluntness of the object facing
the air stream. R~lljstic coefficient controls the maximum rate at which an
object will fall through a still column of air. Because the resistance of an object
through the air increases with velocity, an object which is accelerated by the
earth's gravil~lional force eventually reaches a velocity where the accelerationforce of gravity is balanced by the drag force of the air through which the object
is moving.
This principal is used to separ~le the granulamllaterial into two or more
co",,~o"ents based on the bal~ictic coefficient of the granules. By introducing
the granules into an upwardly moving stream of air which has a velocity which
is greater than the terminal velocity of some of the particles and less than theterminal velocity of other pa, l;GIeS~ the granular material will be separated into
two fractions. Thus, for separating wood chips from wood knots, an air velocity
in the range of four to five thousand feet per minute is chosen which exceeds
the terminal ve!ocity of the wood chips, thereby causing them to rise to the topof the air chamber and be transp,orted through a duct to a cyclone. On the
other hand, the knots, which have a ter",i, lal velocity greater than four to five
~20 13 39
WO 96/09901 PCT/US95/12095
thousand feet per minute, fall through the air to exit the bottom of the
separation chamber.
An exemplary problem addressed by the low velocity air density
separator 20 is separating shredded paper from shredded plastic. The
recycling of post-consumer plastic bottles has resulted in a feed stock formed
by the shredding of plastic milk boffles or plastic pop bottles. The feed stock
contains both plastic from the bottles and paper from the labels associated withthe bottles. In order to make the feed stock a product with an economic value,
it is necess~ry to separate the paper from the plastic. Because the plastic
shards 54 as seen in FIG. 2 are of a thicker gauge of material than the paper
or light grade plastic labels, they have a higher b~llistic co-efficient and can be
separated in theory in an air density separator. However, both the plastic and
the paper are of relatively low ballistic coefficient and so the velocity of the air
in the air density separator must be in the range of five hundred to a thousand
feet per minute, preferably in the range of seven to eight hundred feet per
minute. The problem with these low velocities can be readily demonstrated by
taking a handful of paper confetti such as the punchings from a paper punch
and dropping them into the air. Some of the paper punchings will become
dispersed and rapidly reach their terminal velocity and slowly settle to the floor.
Others, however, will clump together and fall as a unit reaching the floor first.
Thus, it is observed with lightweight materials, they must be adequately
dispersed in the column of air moving up through the vertical separation
chamber 24 if it is desired to reliably separate them on the basis of their
ballistic coefficients.
In the air density separator 20 proper dispersion is accomplished by the
grill 36 formed of closely spaced narrow bars 38. In a chamber having
dimensions of approximately fourteen inches by twenty-six inches, the bars 38
would have a depth of one and a half inches with a thickness of one and a half
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WO 96/09901 PCT/US95112095
to three millimeters and a bar to bar gap of between one-eighth and one-fourth
of an inch when used with a shredded material 44 having an average size of
one-quarter inch to one half inch.
The bars 38 are formed into the grill 36 within a frame 64. One or more
transverse reinforcements (not shown) may be installed on the underside of the
grill 36 formed by the bars 38.
A low velocity air density separator 20 as shown in FIG. 1 was
constructed with a fan 30 of five horse power capability. Table 1 lists the
pe, ro"nance parameters of the five horse power fan. The suction pressure
head was measured at the fan 30. This measurement was used to esli"~ale
the velocity in feet per minute and the flow rate in cubic feet per minute through
the separation chamber 24. Tests were run with shredded plastic containing
paper to detel",i"e the optimal fan operating level which would effect a clean
separation between the paper and the plastic.
TABLE 1
Suction Pressure HeadAir velocity (Ft./Minute)Flow rate (CFM)
~1 of H2O 869 2 140
2" of H2O 825 2 030
3" of H2O 784 1 530
4" of H2O 739 1 800
5" of H2O 695 1 710
6 of H2O 656 1 615
7 of H2O 609 1 500
~ 8" of H2O 559 1 375
For the particular system employed which has an air separation chamber 24
with internal dimensions of 13.75 inches by 25.75 inches a static head at the
fan of four inches of water was found to produce a good separation between
the paper and the plastic.
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WO 96/09901 PCT/US95/12095
As shown in FIG. 2, shredded plastic and paper is fed on the chute 60
onto the deck 62 of the grill 36. The chute 60 extends partially over the grill 36
within the separation chamber. To prevent buildup of material on portions of
the grill not within the chamber a cover 63 may be provided. The vibrating grill36 disperses the granular material across the deck. The air ~ a", which
p~-sses up through the bars 38 of the deck lofts the lightweight paper 56 and
entrains it in the flow of air. The heavier plastic 54 slides through the bars and
drops out the open end of the duct 22.
TABLE 2
PAPER PLASTIC
1500#/HR 5.8% 94.2%
2000#/HR 5.7% 94.3%
2500#/HR 5.3% 94.7%
Table 2 summarizes the results of three tests which were run with
twenty pound samples in the air density separator 20. When a shredded
mixture of plastic and paper having a bulk density of 18.5 pounds per cubic
foot was fed at a rate of fifteen hundred pounds per hour into the separation
chamber, 5.8 percent of the material was recovered from the cyclone as paper
and 94.2 percent was recovered from the bottom of the separation chamber
and consisted of plastic.
Similarly, the test was run at feed rates of two thousand pounds per
hour and twenty-five hundred pounds per hour. A slightly lesser amount of
paper was recovered at the higher rates. It appears separation of the paper
from the plastic is slightly less effective at higher rates. Visual inspection of the
separated plastic and paper indicated that approximately ninety-five to
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WO 96/09901 PCT/U~95/12095
ninety-eight percent of the paper was removed from the plastic and only zero
to one percent of the plastic was lost with the removed paper.
The air density separator 20 inlet 40 does not require an air lock
because of the relatively low velocity of the air. The relatively small effect that
openings in the wall 70 of the conduit 22 have on the stream is utilized to allow
an oversize tray 72 to extend from the deck 62 of the grill 36 through the wall
74 opposite the inlet wall 70. Trash which has become included in the granular
material 44 traverses the sloped grill 36 and exits the duct 22 on the chute 72
which directs the trash for collection in a reject bin 78, as shown in FIG. 1.
The cyclone 28 uses centrifugal forces to separate the majority of the
particulate material from the air stream. The cyclone has an air lock 80 which
allows the paper to be removed from the cyclone. The air that is withdrawn
from the cyclone p~sses through the fan and then into a bag house (not
shown) where any residual dust is removed before venting to the al",osphere.
It should be understood that the low velocity air density separator 20
may employ a rc,rair,i"ous member of configuration other than a grill of narrow
bars. For example, the rorar"i"ous member could be a vibrating screen, or a
vibrating plate with holes punched therein. In addition, the foraminous member
could consist of an interdigitating bar screen with alternating bars osc~ ting
one hundred eighty degrees out of phase with respect to adjacent bars.
It should also be understood that although a separation chamber 24 of
approximately 10 feet in height has been illustrated, the separation chamber
may be shorter or longer.
It should also be understood that the low velocity air density separator
may be used to separate products other than shredded post-consumer plastic
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WO 96/09901 PCT/US95/12095
containers. For example, the density separator 20 has utility for separating dirt
and sand from wood chips.
It should be understood that wherein the term vibration is used, it is not
limited to the vibratory action in a vertical plane produced by the solenoid
arrangement shown in FIGS. 1 and 2 but encomp~sses vibrating in all planes
and oscill~tory motion such as employed by a bar screen.
It should be understood that although coil springs are shown resiliently
mounting the grill foraminous member 36 for vibration, other mounts, for
example leaf springs, are acceptable.
It should further be understood that wherein a solenoid driven by sixty
hertz line frequency causes the foraminous member to vibrate at sixty hertz,
the grill 36 could be caused to vibrate at other frequencies and other
mechanisms for causing the vibration could be employed including a drive
employing eccentric weights, cam followers on a crank shaft, piezoelectric
actuators and systems c~ ~sed to vibrate by high amplitude low frequency air
pressure waves including sound waves.
It is understood that the invention is not limited to the particular
construction and arrangement of parts herein illustrated and described, but
embraces such modified forms thereof as come within the scope of the
following claims.
