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Municipalities are handing recyclers a double-edged sword
as more of them shift to single-stream glass recycling. Single-stream
makes it easier for households to set aside glass recyclables,
increasing the amount of raw materials for sale to glass manufacturers.
But the resulting commingled mess has created new challenges
“Even though single-stream is on the rise,”
says Felix Hottenstein, sales director at MSS, Inc., a glass
sorter manufacturer in Nashville, Tennessee, “there
may not be quite as much glass out there, because much of
it gets lost in the processing.”
The problem also lies with compactor trucks that pick up
and cart the glass. Some vehicle types are more likely to
crush the glass, making it harder to separate the three different
glass types. Commingled glass produces uneven color quality
while metal and ceramic create weakness. Trucks can also cause
cross-contamination with other waste, including plastic and
Consumers who put heat-resistant glass such as Pyrex and
Visionware in recycling bins give recyclers another issue.
"This glass causes big trouble once it’s fed back
to the glass furnace as it does not melt and therefore clogs
the glass production machines," says Peter Mayer, manager
of sorting technologies at S+S Separation and Sorting Technology
GmbH, a manufacturer in Schoenberg, Germany. S+S makes the
Varisort X, which helps recyclers keep such dangerous offenders
out of the waste stream. The company also produces Spektrum,
a camera-equipped color sorter designed for mixed glass.
AI Inc., a manufacturer in Laurel, Maryland, is another company
that specializes in handling heat-resistant glass. “The
problem is growing, and is showing up more and more as costly
product rejects, and has the potential to damage furnaces
and extruding equipment,” says Julie Villescas, sales
manager at Austin AI. The company’s QXR-G uses X-rays
to pull recyclable glass away from metals and other unwanted
glass types, including ceramics, crystal and plate glass.
The QXR-G works on glass before or after crushing equipment,
and detects glass contaminants as the materials move onto
slide-ways or conveyors and then diverts them away from the
processing line. The task takes about 0.14 of a second, according
to the company.
The more glass is processed with products like the QXR-G,
Villescas says, “the fewer the product rejects and the
higher the customer satisfaction.” Newer models of the
company’s machine incorporate more and smaller diverters
to pull off contaminates. “This will minimize the amount
of good cullet material that is pulled off to insure the contaminant
was removed,” she says.
Cullet, which is recycled glass ready for the furnace, is
the highest value end product in glass recycling. Glass manufacturers
like it because it has lower melting temperatures and requires
less energy to process than raw materials. For every 10 percent
of cullet used, manufacturers save up to 3 percent in energy
costs and 15 percent in material savings, according to Austin
How satisfied recyclers are with the sorting process also
depends on what happens to glass before it gets to the sorters.
“Generally all sorting equipment works best with uniformly
sized materials,” Villescas says. “This is one
reason why they are typically placed downstream of a crusher.
Generally some screening to remove fine, or dust material
is performed.” Items can’t be too large or too
small, and vacuuming must be used to remove labels and plastic
As the quality of recovered glass improves, the larger the
market will become and the more post-consumer recycled glass
will enter the marketplace. "Green glass production is
up to 100% of recycled glass being reused," Mayer says.
"This is a real closed loop recycling process."
Other technologies in glass sorting include computer-operated
cameras, light emitting diodes (LEDs) and laser detection.
Metals and color contaminants can be sorted away from the
waste stream via magnetic separators, eddy current systems
and optical inspection equipment. Glass, ceramic and crystal
requires separate solutions such as LED and spectrometry identification
and sorting technologies in addition to newer applications
such as X-ray.
Metal separators use high-frequency detectors down to 0.6
mm. A directed air stream blows out impurities to preserve
as much of the glass as possible. Lasers work by identifying
nontransparent materials such as ceramic, stone, porcelain
and labeled glass. Unwanted materials are then ejected by
CCD cameras equipped with colored filters watch for glass
of varying colors and link to machine settings that separate
the glass into batches of clear, green or brown. S+S's Spektrum
runs with programmable software that will sort one type of
glass from the rest or create three separate piles for each
major color group.
MSS’s GlassSort and Glass ColorSort systems were recently
upgraded from halogen to LED technology to boost accuracy.
High-intensity LEDs flash through the glass to highlight color
differences. The Glass ColorSort modules remove ceramic and
metal at 15 tons per hour and separates colored glass up to
6 tons per hour.
MSS also manufactures a glass bottle sorter that handles
up to 75,000 bottles per hour. Bottles travel along individual
slides fed by a vibrating feeder. As bottles exit the slide,
computerized sensors assess color. A blast of compressed air
ejects the bottle to its appropriate color batch.
New sensor technologies and more precise image processing
continue to advance. New markets may also be on their way.
California currently sponsors a program that encourages brick
and tile manufacturers to include low-value mixed glass in
their products. Faster, more efficient machines aim to increase
the amount of recovered glass from municipal solid waste.
As glass manufacturers forge new markets, new sorting technologies
pay off fasters. Recycled glass can now be found in roadbed
material, filter sand for septic systems and pools, playground
sand, sidewalks and driveways, backfill, drainage systems,
landscaping, paint, hybridized cement, aggregate in stucco
finishes, flux in ceramic tiles, sand blasting material, fiberglass,
marbles, glass beads, lawn ornaments, stepping stones and
retaining wall blocks.
Andela Products Ltd.
Austin AI Inc.
+47 23 30 23 30 (Norway)
S+S Separation and Sorting
+49 8554 308-121 (Germany)