Note: Descriptions are shown in the official language in which they were submitted.
CA 02310169 2000-OS-30
TITLE: ~ COMPOST PARTICLE SEPARATION UNIT
INVENTORS: Gary Nethercott & Les Zinn
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method for separating
plastic material from an organic compost plastic mixture.
Most residential organic yard waste is collected in large plastic bags.
Typical
organic yard waste includes tree branches, leaves, grass clippings and the
like. The plastic bags of organic waste are subsequently placed at the curb to
be collected by municipal waste collection services for disposal. Instead of
being taken to overcrowded landfills, such organic yard waste is capable of
being used as compost which is also better for the environment.
Furthermore, compost which is free of non-biodegradable matter or impurities
such as plastic, is commercially valuable. Current commercial composting
operations arising from plastic bag collection of organic yard waste, result
in
impure compost since the plastic bags are shredded along with the organic
material contained within. The presence of plastic material in the compost
significantly diminishes its value.
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Despite the availability of bio-degradable plastic and paper bags for organic
yard waste, such bags have not gained widespread acceptance among
consumers because of their higher cost and unreliability. The shelf life for
such bags is short and they tend to rip easily or fall apart when exposed to
the elements. Existing methods available to separate the plastic component
from the shredded compost-plastic mixture include removing the plastic by
hand, the use of gravel style vibrating screens and the use of revolving
topsoil
screens. These methods are relatively costly or labour intensive and,
moreover, are not totally effective in producing a plastic free compost
product.
The present invention, which we have named a Compost Particle Separation
Unit (hereinafter CPSU), is intended to overcome the disadvantages of the
prior art described above. The object of the present invention is to provide
an
efficient and effective means of obtaining high quality compost product, free
of plastic contamination. This object is achieved by using the CPSU to
separate the plastic particulate from the commercially valuable organic
compost.
According to the invention, the shredded compost-plastic mixture is deposited
into the CPSU in batches. The CPSU is then used to separate the mixture
into a number of commercially useful products such as, oversize bulking
agents, standard bulking agents, coarse compost, fine compost, and plastic.
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Oversized bulking agents include, for example, tree limbs. Standard bulking
agents include, for example, wood chips. It is the fine compost product,
however, which is particularly valuable.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an improved apparatus for
separating plastic material from a shredded compost plastic mixture and
method of using the apparatus to achieve plastic separation. We have
named this apparatus a Compost Plastic Separation Unit (CPSU).
The CPSU according to this invention has several stages including a first
stage separation unit and a second stage separation unit. Prior to using the
CPSU, organic yard waste is collected in plastic bags. The plastic bags and
organic waste contained within are then shredded by conventional means
resulting in a shredded compost plastic mixture. Initial separation of larger
objects from the mixture is achieved by means of a grate positioned over a
hopper into which the mixture is delivered. Next, a continuous stream of
shredded compost plastic mixture is sequentially delivered to the first stage
separation unit from the hopper by a system of conventional conveyors. The
first stage separation unit operates to separate the coarser compost
component from the compost plastic mixture.
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The first stage separation unit is generally comprised of a vertically aligned
elongated walled vessel having a substantially circular cross-section. The
vessel has an intake opening portion and intake opening at the top, an
exhaust opening portion and exhaust opening at the bottom, and a body
portion between the intake opening portion and exhaust opening portion.
Housed within the vessel is a rotatable platform, a pipe having a
substantially
circular opening at the top thereof, air jet nozzle means circumferentially
arranged in the body portion, and suitably adapted support members.
The rotatable platform is horizontally aligned and substantially circular. The
diameter of the platform is less than the diameter of the vessel, thereby
forming an annular opening. As well, the top surface of the platform is sloped
downwardly from its center and attached to the top surface of the platform is
a
plurality of fins at regular angular intervals.
During operation of the CPSU, a continuous stream of compost plastic
mixture is deposited onto the top surface of the rotating platform. In
response
to the rotation of the platform, the compost plastic mixture is peripherally
and
uniformly ejected against the inner surface of the vessel wall. The compost
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plastic mixture then falls along the vessel wall under the force of gravity,
through the annular opening, into the body portion of the vessel.
The circular opening of the pipe is located underneath the rotatable platform
5 and has its axis in alignment with the longitudinal axis of the vessel and
rotatable platform. Attached to the base of the pipe is an interconnecting
duct
system leading to the second stage separation unit. A material handling fan,
located within the duct system generates a suction effect or area of lower
pressure surrounding the opening of the pipe by drawing a continuous volume
of air into the vessel and subsequently into the pipe through its opening. The
lighter fine compost and plastic components of the compost plastic mixture
are thereby caused to move towards the lower pressure area and form part of
an air stream flowing into the pipe. The air stream, which is drawn into the
opening of the pipe by the material handling fan, thus captures the lighter
fine
compost and plastic components of the compost plastic mixture and carries
them into tt~e pipe.
The air jets are supplied with a source of pressurized air and the nozzles of
the air jets are angled diagonally upwards towards the longitudinal axis of
the
vessel. The air jets perform a number of functions including helping to direct
the falling compost plastic mixture, specifically the lighter fine compost and
plastic towards the opening of the pipe. As well, the air jets aid in
separating
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the compost plastic mixture by drying the mixture and also by air agitation
and
turbulence.
The coarse compost component, which is too heavy to be captured by the air
stream and drawn into the pipe, continues travelling downwardly through the
vessel under the force of gravity. It exits the vessel through the exhaust
opening onto a conveyor leading away from the CPSU.
The fine compost and plastic material suspended in the air stream and drawn
into the pipe is transported by means of the interconnecting duct system to
the second stage separation unit for further separation. The fine compost and
plastic is exhausted into the second stage separation unit, which is comprised
of an air chamber. Within the air chamber, a cyclone separates the fine
compost from the plastic. The fine compost and plastic slide down the
tapered walls of the air chamber and exit through an exhaust opening at the
base thereof onto a downwardly inclined vibrating screen.
Final separation of the compost from the plastic is achieved by sifting the
fine
compost through the perforations of the vibrating screen. The separated fine
compost and plastic components are collected on conventional conveyors
and carried away from the CPSU.
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BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, which form part of the specification and
are to be read in conjunction therewith and in which like reference numerals
are used to indicate like parts in the various views.
Figure 1 is a schematic sectional view of the Compost Particle Separation
Unit.
Figure 2 is a schematic sectional view of the first stage separation unit.
PREFERRED EMBODIMENT
Turning now to the drawings in greater detail and initially to Figure 1, the
Compost Particle Separation Unit (CPSU) has several stages. It is generally
comprised of a grate 1, a hopper 2, a first stage separation unit 3, a second
stage separation unit 4, a material handling fan 5, a duct system 6, and a
number of conventional conveyors, for example at 10 and 11. The conveyors
carry the compost-plastic mixture between initial stages of the separation
process and separated materials away from the CPSU.
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Prior to being processed by the CPSU, the plastic bag and organic material
contained within is shredded by conventional means resulting in a shredded
compost plastic mixture. The shredded organic waste consisting of tree
limbs, leaves, grass and the like, as well as any plastic material, is
sequentially deposited into the hopper 2 by a loader. A grate 1 comprised of
regularly spaced parallel bars positioned over the intake opening of the
hopper permits only material of a predetermined size to pass through. More
specifically, it functions to separate larger objects, for example tree limbs,
from the smaller shredded compost and plastic material. The removal of
objects larger than approximately four inches in diameter is necessary at this
time, as such objects may plug the first stage separation unit 3. The larger
objects, which are denied entry into the hopper 2 remain on the top surface of
the grate 1 and must be manually removed and collected.
The smaller sized material, which is a compost-plastic mixture, passes
through the bars of the grate 1 and enters the hopper 2. The hopper is
preferably capable of holding six yards of material. Material in the hopper is
funneled onto a first conveyor 10, which is located below the exhaust opening
at the base of the hopper. The conveyor is approximately three feet in width
and operates substantially parallel to the ground. It is hydraulically driven
and
the speed of the belt is variable. The stream of compost-plastic mixture
carried by conveyor is approximately three feet deep and three feet in width.
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During typical operations, the speed of the conveyor can be adjusted to
accommodate between 60 and 100 yards of compost-plastic mixture per
hour.
The first conveyor 10 carries the compost-plastic mixture to a second
conveyor 11, which is inclined upwardly with reference to the first conveyor.
The second conveyor is only two feet in width and is, therefore, narrower than
the first conveyor. The stream of compost-plastic mixture carried by the first
conveyor is funneled onto the second conveyor by two angled plates 13. The
second conveyor carries the compost-plastic mixture upwardly to the first
stage separation unit 3. The first stage separation unit is described in
greater
detail later.in the specification.
Preferably, the second conveyor 11 operates at a speed approximately six
times greater than the first conveyor 10. The increased speed of the second
conveyor acts to thin out the stream of compost plastic mixture being
transported to the first stage separation unit 3. In the example given, the
compost-plastic mixture carried on the second conveyor is approximately 1.2
feet deep and one foot in width. The purpose of thinning out the compost-
plastic mixture is to deliver a more even and controlled flow of the mixture
into
the first stage separation unit.
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The first stage separation unit 3 acts to separate the coarser compost
component from the compost-plastic mixture. The first stage separation unit,
shown enlarged in Figure 2, is comprised generally of a vertically aligned
elongated walled vessel 20. The vessel has an intake opening portion 21 at
5 the top, an exhaust opening portion 22 at the bottom, and a body portion 23
therebetween. An intake opening 25, forming part of the intake opening
portion is located at the top of the vessel, and exhaust opening 26, forming
part of the exhaust opening portion is located at its base. The first stage
separation unit is further comprised of a substantially circular rotatable
10 platform 30, a centrally located circular pipe 31, a plurality of high-
pressure air
jets, for example at 35A, 35B and 35C, and suitably adapted support
members, for example at 34A and 34B. Each of these constituent parts is
housed within the vessel and is hereinafter described in greater detail.
Referring tQ Figure 2, the rotatable platform 30 is horizontally aligned and
is
rotatable about its center axis. Furthermore, the center axis of the platform
and the center axis of the circular pipe 31 are in alignment with the central
axis of the vessel 20. The circular pipe, which is located within the body
portion 23 of the vessel, has an intake opening 31A at the top thereof. The
intake opening of the circular pipe is located underneath the rotatable
platform. The diameter of the circular pipe 31 is less than the diameter of
the
rotatable platform 30.
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The operation of the first stage separation unit relies on a material handling
fan 5 (shown in Figure 1). The material handling fan moves a volume of air
through the first stage separation unit at all material times and creates a
suction effect or area of lower pressure surrounding the intake opening of the
circular pipe 31A. The lighter fine compost and plastic components are drawn
into the circular pipe 31 and subsequently transported to the second stage
separation unit 4 (shown in Figure 1) for further separation. The heavier
coarse compost falls downwardly and exits the first stage separation unit
through the exhaust opening 26 at the base of the vessel. The operation of
the first stage separation unit is hereinafter described in greater detail.
Referring still to Figure 2, a stream of compost-plastic mixture is delivered
to
the first stage separation unit through the intake opening 25 at the top of
the
vessel. Located within the intake opening portion 21 is the rotatable platform
30, which is approximately 5 feet in diameter. After entering the vessel, the
incoming stream of compost-plastic material falls under the force of gravity
onto the top surface of the platform. The stream of compost plastic material
is naturally.divided in half with reference to the platform since each half of
the
stream falls onto the corresponding half of the platform. The splitting of the
compost-plastic mixture into two streams in the manner described, achieves a
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more uniform distribution of the mixture on the top surface of the rotatable
platform.
The center of the rotatable platform 30 is preferably raised with reference to
the outside of the platform, thereby forming a downward slope from the
center. The rotatable platform has suitable means to adjust and control the
speed of rotation. Furthermore, the top surface of the platform has a
plurality
of fins, for example at 40, disposed at regular angular intervals. The fins
extend vertically at substantially 90 degrees with reference to the top
surface
of the platform. As such, the top surface of the rotatable platform is not
only
sloped downwardly but also compartmentalized.
After the compost-plastic mixture is deposited onto the rotatable platform 30,
the material is distributed outwardly by means of a centrifugal force and is
peripherally ejected against the inner wall surface of the vessel 20. The fins
40, described above, aid in the peripheral ejection of the compost-plastic
mixture. The compost-plastic mixture is, therefore, uniformly distributed 360
degrees against the inner wall of the vessel by the rotatable platform. It
also
has the effect breaking apart some of the larger pieces of compost, which in
turn helps to loosen the plastic from the organic material.
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As described, the center axis about which the platform 30 rotates is
vertically
aligned with the central axis of the vessel 20 and the diameter of the vessel
is
greater than the diameter of the rotatable platform. The difference in
diameter
between the rotatable platform 30 and the vessel wall creates an annular
opening 41 allowing the compost-plastic mixture to enter the body portion 23
of the vessel. The peripheral ejection of the compost-plastic mixture against
the vessel wall, therefore, has the further effect of uniformly delivering a
volume of material to the body portion of the vessel through the annular
opening.
Within the body portion 23 of the vessel, the compost-plastic mixture falls
along the inner surface of the vessel wall under the force of gravity. A
plurality of high-pressure air jet nozzle means, shown for example at 35A,
35B and 35C, are circumferentially arranged within the body portion of the
vessel. The air jet nozzle means are supplied with a source of pressurized air
and direct air diagonally upwards, towards the central axis of the vessel and
intake opening of the circular pipe 31A. The function of the air jets is to
further separate the plastic from the organic material by air agitation and
turbulence. The jets also have a drying effect, which further facilitates the
separation of the plastic component from the organic material since moisture
and electrostatic attraction tends to adhere the smaller fine compost
particles
to the plastic material. Additional air jets may be used on the supporting
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members of the first stage separation unit, for example at 34A and 34B, such
that plastic~will not wrap or collect on support bars.
The circular pipe 31, which is vertically aligned along the central axis of
the
vessel 20 has a diameter less than the diameter of the rotatable platform 30.
The material handling fan 5 operates to draw air into the circular pipe by
creating a suction effect or area of low pressure surrounding the intake
opening of the circular pipe 31A. The lighter fine compost and plastic
material
moves naturally towards the lower pressure area. The air stream drawn into
the circular pipe captures and carries the fine compost and plastic material
through the circular pipe and subsequently to the second stage separation
unit 4 by means of a suitable interconnecting duct system 6, as shown in
Figure 1. The air stream which travels through the duct system carries fine
compost and plastic to the second stage separation unit, where further
separation of the compost-plastic mixture occurs. The material handling fan
5, which operates at 15,000 CFM is located outside of the first stage
separation unit 3 within the duct system 6. The duct system consists of
conventional ducting and is comprised, for example, of circular or rectangular
type ducts, or a combination thereof.
An additional purpose of directing the air jets 35 slightly towards center is
to
direct the compost-plastic mixture, specifically the lighter plastic and fine
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compost components towards a deflector plate (not shown in Figures) located
inside the body portion 23 of the vessel. Specifically, the deflector plate is
located below the rotatable platform and above the intake opening of the
circular pipe 31A. This deflector assists in the separation of the fine
compost
5 and plastic by directing the compost-plastic mixture towards the intake
opening of the circular pipe 31A and previously described area of low
pressure created by the material handling fan 5.
Referring to Figure 2, the coarse compost component, which is to heavy to be
10 drawn into the circular pipe 31 exits the vessel 20 by means of the exhaust
opening 26. The vessel, specifically the exhaust opening portion 22, is
inwardly tapered towards the central axis. Coarse compost exiting at the
base of first stage separation unit is for convenience deposited on a conveyor
(not shown in Figures) to be carried away from the CPSU. The coarse
15 compost component is largely free from plastic contaminants since most of
the plastic material was removed and carried away in the manner described.
Referring once again to Figure 1, the material handling fan 5 is located
within
the interconnecting duct system 6. The air stream generated by the material
handling fan carries fine compost and plastic within the duct system from the
first stage separation unit 3 to the second stage separation unit 4. In the
section of the duct system between the first stage separation unit and the
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material handling fan 5, the fine compost and plastic mixture is drawn towards
the material handling fan in response thereto. The fine compost plastic
mixture subsequently passes through the material handling fan and is blown
upwards into the second stage separation unit.
Referring to Figure 1, the second stage separation unit 4 acts to separate the
plastic component from the fine compost component. Within the second
stage separation unit a vortex air chamber 50 helps to further separate the
organic compost material from the plastic. The air is exhausted out of the top
of the second stage separation unit while the fine compost and plastic collect
around the outside of the cyclone and slide down the inner surface of the
chamber wall under the force of gravity. The strong action of the cyclone and
the force exerted of the compost-plastic mixture when it comes in contact with
the chamber wall act to separate the fine compost from the plastic. The fine
compost material and plastic material drop out the bottom of the second stage
separation unit and exits the chamber through a sized discharge elbow (not
shown in Figures).
After exiting the discharge elbow, the fine compost and plastic is deposited
onto a downwardly inclined 118" vibrating screen (not shown in Figures). At
this stage, most of the plastic is in a loose fluffy state and is on top of
the fine
compost. The fine compost is sifted through the perforations of the screen
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onto a conveyor positioned below. It is then carried away from the CPSU
where it can be collected in a pile or appropriate container. The fine compost
is close to 100% free of plastic material. The plastic material continues
downwardly along the inclined screen aided by the vibrating action where it is
ultimately deposited in a collection box to be appropriately disposed of.
From the foregoing, it will be seen that this invention is one well adapted to
attain all the ends and objects hereinabove set forth together with other
advantages which are obvious and which are inherent to the structure.
It will be understood that certain features and sub-combinations are of
utility
and may be employed without reference to other features and sub-
combinations. This is contemplated by and is within the scope of the claims.
Since many possible embodiments may be made of the invention without
departing from the scope thereof, it is to be understood that all matter
herein
set forth or shown in the accompanying drawings is to be interpreted as
illustrative and not in a limiting sense.
