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MRF operators say improved optical sorting technology is helping them meet tougher domestic and international quality expectations.

Brian Taylor March 5, 2014

Throughout 2013, operators of material recovery facilities (MRFs) huddled with their operations staff and equip- ment vendors to make adjustments in response to China’s Operation Green Fence.

Green Fence, which went into effect in 2013, introduced a painstakingly thorough new inspection regimen in China that increasingly treated loads and bales of recyclables as potential “solid waste” shipments subject to rejection.

Even before Operation Green Fence, Chinese regulations had discouraged the importation of bales of No. 1 PET (polyethylene terephthalate) and No. 2 HDPE (high-density polyethylene) food- and beverage-contact containers. Many buyers and sellers, however, had been trading in post-MRF mixed plastic bales that typically contained a variety of plastics No. 3 or No. 4 through No. 7.

The implementation of Operation Green Fence caused the mixed No. 3 through No. 7 grade to lose a major outlet and caused some MRF operators to experience a realization: Whether their baled plastic containers were being sold domestically or they were shipping them internationally, it was increasingly vital to boost the quality of those bales to minimize the presence of contaminants.

“In order to meet Green Fence’s higher quality standards, many MRFs have slowed down operations to improve container separation and quality,” says Sean Duffy, president and CEO of MRF operator ReCommunity, Charlotte, N.C. “Additionally, Green Fence has added administrative costs because of new procedures and tasks to ensure quality.”

Duffy says ReCommunity had been emphasizing quality before Operation Green Fence was enacted and it also had a head start on investing in optical sorting equipment.

The investments in optical sorting have continued at MRFs run by ReCommunity and other companies as the technology has become faster and more thorough, according to recyclers.
 

Making the grade

The residential recycling stream yields a variety of plastic containers of different resins and colors, many that once contained beverages or food and others that once held soap or detergent.

Keeping hope alove for No. 5

In the United Kingdom, Axion Consulting (www.axionconsulting.co.uk) has been working on behalf of WRAP (the Waste & Resources Action Programme) to find solutions for turning scrap No. 5 polypropylene (PP) food containers back into new food-contact-grade plastic.

Axion says its research focused on developing an automatic process that uses diffraction gratings to identify and separate PP that has been in contact with food from PP scrap that has not.

“Under European food packaging regulations, only PP that has been in prior contact with food can be recycled into new food grade PP,” says Axion in a news release summarizing the project.

(Full details of WRAP’s research project managed by Axion can be found in WRAP’s report at www.wrap.org.uk/sites/files/wrap/Diffraction%20grating%20
report.pdf
.)

For the postconsumer sorting process to work, food-contact PP packaging material must first be manufactured with lines (a diffraction grating) that can be scanned by a laser to reflect a specific pattern.

At recycling plants, “the pattern is then captured by a camera connected to a computerized image recognition system that is able to identify the marked food contact PP packaging,” Axion says. The company says the technique is potentially applicable to other polymer types, including high density polyethylene (HDPE) and polyethylene terephthalate (PET) packaging.

“Manual sorting is simply too expensive,” says Axion chemical engineer Richard McKinlay, who helped build the demonstration unit for the project. “Diffraction is when one beam of light is split into several, so we are utilizing this phenomenon to detect a particular type of plastic packaging,” he adds.

In its pioneering stage, Axion estimates a single diffraction grating sorting unit, including conveyors and ancillary equipment, can be installed for $815,000, with a potential payback within four years. Recyclers with access to baled PP food container scrap will likely have to work with new food container manufacturers to help ensure such a payback.

“Challenges remain, including the need to widen applications and markets for this technology,” says Axion Senior Consultant Liz Morrish. “It is also crucial for retailers, manufacturers and machinery suppliers to adopt agreed industry-wide methods that would optimize the identification and subsequent recycling of these waste streams.”

Recyclers in the trenches who must produce secondary commodities while maintaining a profit margin will be the ultimate judges as to the effectiveness of this emerging sorting technology, as they have with so many others.

This variety of plastic scrap comes in mixed and commingled with paper and glass, presenting the challenge of properly sorting it into marketable grades that can meet the quality specifications of buyers.

Duffy says ReCommunity has “typically separated out five different plastic grades, and we have been able to continue marketing these five grades of plastics: 1) No. 1 PET; 2) No. 2 HDPE colored; 3) No. 2 HDPE natural; 4) No. 4 through No. 7 mixed plastic grade; and 5) mixed bulky rigid plastics.”

He adds that although Green Fence has affected demand for the two mixed grades, ReCommunity MRFs continue to sort into these same grades.

Brad Dunn, the Cincinnati district manager for Cincinnati-based Rumpke Recycling, says “Green Fence has been a challenge for the recycling industry as a whole,” with Rumpke seeing “more pressure from exporters demanding increased material scrutiny.”

Rather than sorting into the five grades sought at ReCommunity, Dunn says at Rumpke, “The containers are sorted into three plastic streams; HDPE, PET and No. 3 through No. 7.”

The company does not color-sort its PET to separate out clear bottles at the Cincinnati MRF because nearby consumers will buy mixed PET. “In our area, PET is used primarily for strapping tape and certain textiles, eliminating issues associated with mixed-color PET.”

Although the end goals sought at the ReCommunity and Rumpke MRFs are different, each company has found that optical sorting is now playing a larger role in meeting quality standards.
 

The eyes have it

MRF operators have been investing in (and in some cases experimenting with) optical sorting devices and systems for many years, but confidence in the technology seems to have taken large steps forward in the current decade.

“Optical sorting technology has improved significantly in the last four to five years,” says ReCommunity’s Duffy. “Improvements in camera and information processing technology have added flexibility to target any grade or combination of plastic grades with one sensor.”

Duffy continues, “The best technologies for separating PET bottles are optical scanning sortation systems using near infrared (NIR) transmission and reflection technology.”

Regarding isolating HPDE containers, Duffy says, “Similar to PET sortation equipment, NIR optical sortation equipment is also used for HDPE at a number of our locations where there is sufficient volume to justify the investment.”

Dunn currently helps manage a new MRF near Cincinnati in which Rumpke invested some $32 million. Working with Machinex Industries Inc., Plessisville, Quebec, as its lead vendor, the new MRF was outfitted with several different optical sorting units. The MRF in St. Bernard, Ohio, opened in October of 2013.

“Our new operation features several optical sorters on our container lines,” says Dunn. “We also utilize optical sorters at our Columbus, Ohio, facility. The optical scanner technology ensures significant efficiencies and favorable purity rates. These sorters provide very good container segregation by type with minimal need for quality control hand sorting.”

Duffy says improved optical sorting technology has helped ReCommunity’s network of three dozen MRFs improve plastic container sorting in several ways, including:

  • improved capture rates (typically 92 percent or higher);
  • higher resolution devices mean a wider range of object sizes, shapes and wall thicknesses can be identified;
  • higher throughputs in terms of pieces per minute sorted; and
  • double sortation capability devices can now sort out HDPE color and HDPE natural containers with the same optical sorter.

Dunn says the reliance by MRF operators on optical sorting has been possible thanks to advances made by vendors. “Over the past few years, optical sorting has become more efficient, more accurate and stronger while handling larger volumes of materials,” he comments.

Rumpke has found uses for the improved optical technology beyond sorting its plastics stream. “The ability (if so equipped) to identify the smallest plastics and metals and effectively remove them from other streams in the plant, such as newspaper, is beneficial,” Dunn says. “This not only improves fiber quality but also plastics recovery from that stream.”

At Rumpke’s MRFs, “With the advancements in optical sorting, we have significantly reduced hand sorting,” says Dunn. “On average, Rumpke’s Cincinnati recycling facility will process and sort more than 800 tons monthly of plastic containers from single-stream materials. The containers are sorted into Rumpke’s three plastic streams: HDPE, PET and mixed No. 3 through No. 7. Only one quality control sorter is required for each of these streams and is located past the optical sorters. Typically, this achieves a 97 percent or better purity rate.”

However, room for improvement remains, Dunn says. “Multiple units focused on the same material are sometimes required to perform a ‘double pass’ to achieve the fullest benefit,” he says. “A challenge associated with collateral damage to other materials does exist. For example,” Dunn says, “paper being blown into the container streams [then] requires ejected paper removal mechanically or manually further downstream.”
 

Bolstering performance

With the research and development of optical sorting devices still ongoing, the devices do not operate in a vacuum at MRFs, with mechanical sorting and human hands and vision still a part of the process.

“If necessary, we can sort colored HDPE by hand as an alternative to using dual-valve block units, which typically decrease recovery and material purity,” says Dunn, citing one example.

ReCommunity’s Duffy says the company still relies on trained sorters at picking stations to play several valuable roles in improving material quality, including:

  • quality checks on the “accept” fraction of optical sorting devices to remove any contaminants;
  • quality checks on the “pass” fraction of optical sorting devices to capture any plastic missed by the device;
  • the recovery of plastics with lower volume rates either at a lower throughput facility or of plastics arriving in a lower percentage product (typically No. 3 through No. 7); and
  • the recovery of large and bulky rigid plastics.

The efforts MRF operators have made to introduce more optical sorting and otherwise boost quality have helped them maintain viability in the post-Green Fence era, but those same operators are unlikely to see the job as one that is finished.

“Rumpke has stepped up bale inspection and has gone to great lengths to ensure we have the technology needed to meet [quality] demands,” Dunn says.

With recyclers having no way of knowing what new materials may start arriving in MRFs in 2014 and beyond or what new quality expectations might emerge, they are likely to continue to huddle with vendors and technology providers to meet as yet unknown challenges in the future.

 

A home for higher numbers

Before the advent of China’s Operation Green Fence, bales of mixed plastic containers produced by material recovery facilities (MRFs) in the U.S. were often exported to China, where they were broken and hand sorted.

The Green Fence inspection regimen made such mixed plastic bales increasingly unwelcome, subsequently creating a headache for many MRF operators who had been relying entirely on the Chinese export market.

Among the recyclers and consumers stepping forward to try to fill that niche is EcoStrate SFS, Arlington, Texas.

EcoStrate produces street signs and other products made from mixed plastics, including No. 3 through No. 7 containers. “We can and are doing so,” the company’s Ron Sherga says of EcoStrate’s ability to use mixed containers as feedstock.

More information on EcoStrate’s production process and strategy will be available in the April 2014 edition of Recycling Today in a feature story that will profile the company’s operations and history.

 

 


The author is editor of Recycling Today and can be contacted at btaylor@gie.net.

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