 Introduction
Available sorting systems
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Marker Systems
Where will systems be used?
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In the rnid-l980s, The Society of the Plastics Industry, Inc.
developed a resin identification system compatible with manual
sorting which was designed to help handlers and reclaimers identify
the plastic used in a particular brand or product line. Although
it helped meet an immediate need, everyone acknowledged that automatic
sorting technology would soon be required.
In recycling programs where HDPE milk jugs and PET soft drink
bottles are the only plastics collected, separation is fairly
simple. Reasonable sorting rates of 500 to 600 pph (pounds per
hour) are achieved. But as residents set out more types of plastics,
sorting problems are significantly compounded. Now a variety of
shapes, sizes and colors are added, and decreases in both rate
and quality are common. In addition, because turnover is high
among sorting line workers consistency is difficult to achieve.
The automatic sorting systems being developed by entrepreneurs,
corporations and universities are designed to improve efficiency
and quality, and reduce the cost of plastics recycling. Automatic
plastics separation can be accomplished at three different levels:
macro, micro, or molecular. This report focuses on macro separation
of whole containers.
Macro separation of plastics is the only type of sorting currently
practiced commercially. Manual sorting is macro separation and
is also the first method of sorting that is being automated. The
pioneer in this technology is Prof. Henry Frankel, at the Rutgers
University Center for Plastics Recycling Research. In 1989, with
funding from the Council for Solid Waste Solutions and the Plastics
Recycling Foundation, Dr. Frankel developed a system to separate
PET, unpigmented HDPE and pigmented containers using the light
transmission properties of the resins. During the past three years,
he has brought this concept to a single station, multidetector
system with computer software to track the containers and eject
them by resin and color into separate downtream containers.
Because PET and PVC are contaminants te each other when mixed,
industry pressure for improved quality of the recycled streams
led him the look for a detector that could identify the PVC that
occasionally appeared in the PET stream. He enenuraged Asoma Instruments,
Inc. of Austin, Texas to modify one of its standard
laboratory instruments so that it could respond to this need.
Asoma was able to provide an instrument with an ultra fast analysis
capability (200 analyses per second), so that it could check each
bottle many times as it went by. This made possible accurate identification
of bottles traveling past the detector at high speeds, despite
interference's from labels, dirt, etc. The systems subject the
containers to low-level radiation and the chlorine atoms in the
PVC molecules respond with a unique peak in the x-ray spectrum
which is detected by the instrument.
Significant improvements have been made since the first unit was
sold in 1989. Each of Asoma's Model VS-2's can identify singulated
PVC bottles traveling anywhere in a one foot wide channel at a
speed of 10 feet per second, with a miss rate of less than one
bottle per 100,000. Several units can be placed side by side to
cover wider channels. These units sell for $35,000 to $45,O00.
The limiting factor on accuracy is determined more by the mechanical
details of the material handling system than by the detectors
as is the case for most macro sorting systems.
NRT manufactures machines that process a mixed plastic container
stream at a rate of 2,000 or 5,000 pounds per hour. The 2,000
pph unit sells for under $100,000, and the 5,000 pph unit sells
for under $200,000. The actual price depends on the specific design
parameters. The smaller machine is a new offering, but eight 5,000
pph VinylCycle systems were sold during the past two years.
These pioneering efforts led to the recent introduction of an
integrated high-speed sorting system for the separation of the
four most commonly collected packaging plastics: PET, PVC, HDPE,
and PP. Commercialized with the assistance of the Council for
Solid Waste Solutions, the first such automatic plastic sorting
system was sold to Eaglebrook Plastics in Chicago and started
up in late December 1991. It was engineered by Magnetic Separation
Systems (MSS) of Nashville, Tenn., to scrl 5,000 pounds per hour
of mixed plastic bottles, and consists of four parallel lines
fed by a bale breaker and singulator system. The process works
with either whole or baled bottles.
The MSS «Bottlesort» system employs a primary detector
to separate the bottles into three streams: PET and PVC; unpigmented
HDPE and PP; and mixed color opaque. The process can be designed
to stop at this point or separate the three prirnary streams into
subcategories by the addition of other sensor and eject modules.
Four other modules are available: PVC Module - separates PVC from
PET bottles, PET Module - separates green and amber PET from clear
PET; PP Module - separates unpigmented PP from unpigmented HDPE
and; Color Module - separates mixed color opaque into seven individual
colors or combinations of colors. The system has the ability to
add as few or as many modules as required to handle the incoming
material. It could be designed as a hand-fed, single line handling
1,250 pph using only the primary detector, or a multiline system
integrated with a bale breaker and singulator employing all of
the modules and diverting the separated streams directly into
individual grinders. Costs for these systems would range from
$65,000 for a basic hand-fed detector to $750,000 for a 5,000
pph system with all the options.
A second macro system for sorting baled bottles funded by the
CSWS is being developed by Autornation Industrial Control (AIC)
of Baltimore, Maryland. This system uses a pair of detectors at
a single station - one for determining resin type and one for
identifying color - to control the separation. The system is capable
of detecting and separating all of the common packaging resins
(PET, HDPE, LDPE, PVC, PP, PS) and polycarbonate (PC).
A demonstration line currently is under construction and is designed
to process three bottles per second (approximately 1,500 pph).
The bottles will be carried to the detector by a singulator (equipment
which positions the bottles in a single file prior to the detector)
developed by Chamberlain MRC of Hunt Valley, Maryland, a subcontractor
to AIC. The prototype line, expected to be completed in June 1992,
will be designed to separate bottles into specific categories
of resin/color combinations with one pass. The demonstration line
will provide for separation into seven categories such as clear
PET, natural PP, red HDPE, blue PVC, etc. The categories may be
changed by modifying the computer programs. The cost of the AIC
system will not be determined until after the completion of the
prototype demonstration, but it is anticipated that a basic 1,500
pph system (singulator, detector and diversion system) will be
in the range of $350,000 to $400,000, and 3,000 pph system from
$425,000 to $475,000.
Introduction
NCREASINCLY, designs for large scale materials recovery facilities
specify that the majority of sorting is done automatically. Magnets,
trommels and air jets, for example, separate tin from glass and
cans from plastics. But further separation within categories (paper
by type, glass by color, plastics by resin) continues to be done
by hand. Experts are predicting that this too will soom become
a thing of the past. We are on the verge of a technical revolution
that will extend automatic sorting to individual materials - specially
for plastics.
Available Sorting Systems
National Recovery Technologies Inc. (NRT) of Nashville, Tenn.,
has developed a system called Vinyl Cycle based on a principle
similar to that of the Asoma PVC detector. The system works on
whole or crushed bottles, but does not require that the containers
be delivered single file. Vinyl Cycle consists of a row of detectors
beneath the width of a conveyor belt. When a PVC container passes
over a detector, its position on the belt is noted. The container
is computer tracked and ejected by an air jet further down stream
.Other containers in the proximity of the PVC container are ejected
along with the PVC, so the result is a PVC-rich stream while the
original feed stream is essentially PVC-free. Initial experience
with commercially installed units has shown a better than 99 percent
recovery rate of vinyl containers.