See 'n' sort: optical sorting equipment helps recyclers to sort diverse materials into relatively homogenous commodity streams.

Whether dealing in metals, plastics, glass or paper, recyclers seek to produce consistent, quality secondary commodities that meet the specifications of each of their consumers. This is not a simple task. The job is further complicated in that consumers' specifications for the same end product can vary. For instance, one paper mill may allow a certain percentage of brown envelopes in its office pack, while a second mill may view brown envelopes as a contaminant in its definition of office pack.

While hand sorting may be a viable means of separating materials for a number of smaller processors or material recovery facilities (MRFs), the more tonnage a facility deals with, the more demanding the separation task. For these high-tonnage facilities, automated optical sorting systems may provide an attractive alternative to the legions of hand sorters required to produce consistent streams of quality material.

Tonnage considerations aside, for facilities that see large amounts of broken, mixed glass, optical sorting systems may be the only conceivable means through which to arrive at a saleable, homogenous stream of cullet that can go back to container-glass furnaces.

MRFs and recyclers employing optical sorting equipment ideally can sort divergent materials into relatively homogenous commodity streams that can be marketed more easily and at higher prices.

While still in limited use in light of their high tonnage requirements, optical sorting systems have been used in the recycling industry since the early 1990s.

THE BASICS. Optical sorting equipment was originally targeted to processors of plastics in the early 1990s. The units enable plastics to be sorted by resin type and by color. The technology was then adapted to sort glass by color and to remove ceramic contaminants from the incoming stream of material. In the late 1990s, optical separation technology was modified to differentiate between the various paper grades.

Within the last few years, the market for optical sorting equipment has shifted toward MRFs in part because of the growing trend toward single-stream collection programs. By automating the sorting process, MRFs are able to sort high volumes of incoming materials using fewer employees and with a higher degree of accuracy, according to the equipment manufacturers.

The optical sorting process can be divided in to three main parts: material preparation, identification and separation.

After removing some of the major contaminants, material must be presented to the optical sensors in a single layer for best results, which is similar to the way material is prepared for manual sorting lines. The material is then accelerated through the system using either acceleration conveyors, as in the case of paper and plastic, or vibratory feeders and steep slides in the case of glass.

The optical sensors and their placement vary depending on the material to be sorted. For instance, in the case of glass, color sensors measure the amount of red, green and blue in the glass pieces, accepting or rejecting material based on predetermined calculations. Color sorts for paper may involve CMYK camera technology, which detects the four printing colors--cyan, magenta, yellow and black. Infrared spectroscopy is used to differentiate among resins like PET from HDPE or PVC and to tell different paper fibers apart.

When sorting based on color, the material is looked at using either transmission or reflection. When the transmission method is used, a light is shown through the material, and the sensors analyze the spectrum in the transmitted light. This method is used when sorting glass or colored plastics from clear plastics. When sorting paper by grade or plastics by resin, reflection is used. The sensor is placed above the conveyor, peering down, not through, the material. The sensor analyzes the reflected light spectrum. Air jets ale then used to divert the designated material.

Most optical sorting lines feature easy to-use touch screens and can incorporate pre-programmed sort specifications for particular end users. Weyerhaeuser Co. takes advantage of these pre-programmed sorts at its Denver and Baltimore collection locations.

PAPER SORTING. Weyerhaeuser, based in Federal Way, Wash., is one of the world's largest integrated forest products companies. The company worked with MSS Inc., Nashville, (a subsidiary of CP Manufacturing, National City, Calif.) to develop a paper sorting system for its Baltimore collection center, which has been in operation since 1999. The company added an optical sorting line at its Denver collection center in 2000.

"Baltimore was chosen because of the fact that there is so much high-grade-recovery paper in the lager metropolitan area, especially because of the federal government accounts, which include mostly high-grade office paper," Pete Grogan of Weyerhaeuser says.

"Denver is an important and a good market for domestic mills and for export mills. We have an excellent facility there, and we had plenty of room to install the equipment."

Weyerhaeuser's sorts at these locations vary throughout the course of the day based on the end user's requirements. "The beauty of the optical sorting system is that when our team fires up the equipment in the morning, they can program in the exact requirements of any specific mill using the touch screen," Grogan says. "We are able to sort to end-use mill requirements per customer and to provide a very consistent high quality pack that meets the demands and the requests of the end-user purchasers."

While Grogan is enthusiastic about the PaperSort systems in place at Weyerhaeuser's Baltimore and Denver locations, he was initially skeptical about using optical technology to sort paper grades. "Many people, including myself, thought one could never sort paper mechanically because of all the complications in different grades of paper," he says.

However, Grogan says Weyerhaeuser realized that it would have to improve its long-term paper recovery in light of international demand. The company estimates that this new international demand will require 6 million tons of recovered paper yearly for the next 10 years. "Given the high volumes of paper that were going to need to be recovered," he says, "we couldn't continually depend on hand-sorted labor. We needed to move to a new place. The new place was automated sorting."

The PaperSort systems in Weyerhaeuser's Denver and Baltimore collection centers enable them to be more operationally effective, Grogan says, from a perspective of lowering operational costs and processing material at a more efficient rate.

"That optical sorter can read and sort thousands of sheets per second," he says. "That's a little faster than I can do it."

Grogan says that the response Weyerhaeuser has received from its mill customers has been positive. "The mill operators, if they love one thing, it is a very consistent pack, because then they know how to make the rest of their ingredients and formulas work once they have that consistency," he says.

Weyerhaeuser has compared the results of tests on its hand-sorted bales to those on its optically sorted bales. Grogan says the company has found that the optical sorting system produces a bale of higher quality and consistency than that of the hand-sorted bale.

While Weyerhaeuser has no current plans to add additional optical sorting systems, Grogan says, "We will be giving serious consideration to purchasing future machines." He adds, "We believe that the future is optical sorting for recovery of high volumes of paper."

Optical sorting equipment has helped Weyerhaeuser to produce consistent, high-quality bales for its consumers and to handle increasing volumes of recovered paper. Similarly, optical sorting equipment can help MRFs recover more colorsorted glass, which is easier and more profitable to market than mixed glass.

GLASS AND PLASTICS. Sandy Rosen of Great Lakes International Recycling, Roseville, Mich., says the company is considering adding an optical sorting line to separate glass by color. Great Lakes currently runs material from single-stream curbside programs, which bring in 300 to 400 tons a month of glass. "About 80 percent of that ends up getting broken either through collection or through processing," he says. According to Great Lakes' analysis, 65 percent to 70 percent of the mixed broken glass is flint.

"The mixed broken glass right now has a negative value to us, and the flint has a positive value," Rosen says. "We estimate the difference between the two to be about $40 per ton. We think that this system could save us up to $8,000 each month."

TiTech Visionsort of Norway has nearly 600 optical sorting units in operation worldwide and enjoys 90 percent of Europe's market share. Within the U.S., TiTech has 20 systems in operation. The PREI facility in Raleigh, N.C., a subsidiary of Waste Management's Recycle America Alliance, has had a TiTech system in operation since December of 2000. In 2001, Tom Draney, PREI's general manager at the time, told Recycling Today that the sorting system has a throughput of about 5.5 million pounds (2,750 tons) of plastic containers per month. The system performs a resin sort (PET and HDPE), then a color sort into four streams of natural HDPE, color HDPE, clear PET and green PET.

Van Dyk Baler Corp., Stamford, Conn., is the North American distributor for TiTech Visionsort units.

Todd Heller Inc., Northampton, Pa., operates two optical sorting lines. The company's glass benefication plant has an optical sorter that was installed roughly three years ago that removes ceramics contaminants and then sorts the glass by color. The company's MRF has optical equipment that sorts PET and HDPE containers from a mixed container stream that his been in place roughly two years.

Plant owner Todd Holler says that the incoming container stream, which does not include fiber, enters a pre-sort area. Magnets remove steel containers, and eddy currents remove aluminum containers. The plastic is then perforated and goes through the optical sorting equipment, which separates the PET and the natural HDPE. The company typically processes 10 to 12 tons of containers per hour.

Heller says the company added optical sorting equipment in an effort to make a better product for its customers and to try to manage its labor situation. However, Heller says he has not realized the labor savings that he thought he would.

"You still need that hands-on labor to do quality sorting and to clean up the product. It's not like you just put in the optical sorting equipment and suddenly all of your labor goes away. We still have close to the same amount of labor [that we had before the installation]."

While Heller says the equipment is helpful, he adds, "We really haven", seen the economic benefit." He says part of the reason is because he is paying to dispose of more material at the landfill, particularly in relation to the glass sorting line.

Retrofitting the equipment to Todd Heller Inc.'s existing plants also proved challenging. "It would be much easier if you were starting with a new plant. It gets a little tight trying to retrofit into existing buildings and trying to get material to flow and to leave room for separation and conveyors underneath," Heller says.

He adds that it's important to understand that optical sorting systems are not "magic bullets. They a re not going to solve all your problems."

However, optical sorting systems can provide high-volume, single-stream MRFs and recyclers with a viable alternative to manual sorting.

For companies such as Weyerhaeuser, Grogan says, "I truly think optical sorting is the future. In five or 10 years, the industry at large will look back and wonder how we ever managed the volumes that we did historically without mechanical sorting capabilities."

The author is associate editor of Recycling Today and can be contacted via e-mail at [e-mail].