A Paper Sorting Dream
Jun 9, 2014, 09:10 AM
September/October 2000
Who’d have thought the scrap paper industry would see the day that a machine could do all the sorting? That day is here.
By Aaron B. Pryor
Aaron B. Pryor is associate editor of Scrap.
Five years ago, scrap paper processors could only dream of an automated system that could sort mixed loads of recovered paper into distinct, valuable streams.
At Weyerhaeuser Co.’s paper recycling plant in Baltimore, that dream is now reality.
In 1999, the plant installed a PaperSort line, reportedly the world’s first high-speed automated optical sorting system for recovered paper. The system, developed over five years by Weyerhaeuser and MSS Inc., can sort up to 8 tons an hour, depending on the type of paper being processed and the width of the sorting conveyor. Recovering that much by hand would require eight to 10 employees. With PaperSort, one employee oversees the process, making sure the system runs smoothly from pit conveyor to finished product. And, in the end, the system yields sorted paper streams that can be sold for $80 to $90 more a ton than unsorted material, the companies say.
Is such automation the way of the future for paper sorting? Take a tour of the groundbreaking Baltimore plant and decide for yourself.
Getting Up to Speed
The recovery process at the Baltimore plant begins in much the same way as any hand-sorting operation, with incoming paper being unloaded in a collection area, which takes up about half of the 64,000-square-foot facility.
The operation, which has seven bays for receiving and five for shipping, can accept paper in any form, from bales to loose material in gaylords. Most of its infeed is mixed office paper acquired through contracts with state agencies and other generators.
The company also handles a sizable volume of bound publications, which it must run through a special device to remove the spines, leaving nothing but clean paper to proceed through the PaperSort process.
All incoming paper is fed onto a slow-moving pit conveyor that feeds an inclined lift conveyor. This is where the first critical steps of the PaperSort system begin—reducing the “burden depth,” or depth of paper, on the conveyor and spreading out the individual pieces of paper.
Why is this important? As MSS explains, sorting of any type of material stream requires that the objects be spread out evenly in order for each piece to be correctly identified and separated. Ideally, no piece of paper will overlap another because the sorting sensors identify grades by reading only the top of the items. The goal is to deliver a metered, single-layer stream of paper to the sensors that come later in the process.
The heavy flow of paper from the pit conveyor begins to thin and spread out as it’s fed onto the faster-moving inclined lift conveyor. Level sensors control the burden depth on these conveyors via feedback to the programmable logic controller that determines the speed of both conveyors.
From the inclined lift conveyor, the paper falls onto a large active disc screen, which continues the process of accelerating and spreading out the paper. This specially designed disc screen functions differently than other existing models that screen or sort OCC or ONP. The PaperSort screen looks like an inclined series of spools with brushes that churn back and forth to advance the paper and spread it out flat.
Once the paper leaves the disc screen, it feeds onto a small incline conveyor, which carries the paper onto the high-speed acceleration conveyor on which the sensor stage takes place.
By the time the paper is under the sensor, it will be traveling 1,000 feet a minute—compare that with the 75 feet a minute of traditional manual sorting conveyors. The speed not only increases efficiency, it also aids the process, helping the paper lie flat and in a single layer, which is necessary for the sensor to make a proper scan. To ensure that the fast-moving paper doesn’t shift on or lift from the belt, the process also uses a comprehensive air system and a pinning device, or roller.
The Heart of the Process
It’s at this point where the system’s most innovative technology—the optical sensor—goes to work.
The Baltimore plant initially used only a bright-white sensor, which provided precise identification of paper grades containing optical brighteners. The sensor measured the intensity of the paper’s fluorescence at a specific wavelength in the ultraviolet light.
After a while, though, it became clear to MSS and Weyerhaeuser that they needed a more sophisticated sensor to differentiate nonwhite paper grades.
Enter the MultiGrade sensor, which can classify different paper grades, including solid color sheets, ONP, brown grades, color printed items (such as magazines and newspaper inserts), off-whites, and other coated and glossy papers. To achieve this task, the MultiGrade unit uses a full-range color sensor and enhanced image-processing software, all driven by multiple processors that give it increased computational power, with the ability to process up to 25,000 data points a second.
The MultiGrade sensor also has a near-infrared frequency to sense additional paper “signatures” for more detailed paper-grade classification, as well as a glare sensor to identify glossy coatings or other shiny objects (such as plastic items or films). The sensors are equipped with modems so they can be remotely accessed to download, upgrade programs, or to do diagnostics.
The MultiGrade sensor is especially useful for pulling out prohibitives such as Mylar and Tyvek envelopes. A standard color sensor won’t pick these out, but the MultiGrade’s gloss and infrared sensors, combined with its color sensors, can easily find and eject such products.
Notably, the MultiGrade unit is a “learning” sensor. If the operator wants to introduce a new grade, for instance, the operator can run a sample of that grade through the sensor and it will “learn” the properties of the new grade.
This sensor, which is mounted at the end of the acceleration conveyor, looking down on the belt, consists of 64 detection channels spread evenly across the 4-foot width of the belt (3-foot and 6-foot widths are also available). The sensor scans all 64 detection channels about every 4 milliseconds, which translates to approximately 30 to 40 objects a second. The sensor scans a pixel image three-fourths of an inch square on each piece of paper, then performs image processing to determine the paper grade as well as the size and position of the object on the belt.
Directly downstream from the Multi-Grade sensor, just beyond the acceleration conveyor’s head pulley, is an air-jet sorting unit. Based on information from the sensor, this unit uses its 32 high-speed air jets to eject paper that was classified as “to-be-ejected” into a chute. Paper objects that aren’t to be ejected continue to speed onward onto a take-away conveyor, which is slightly lower than the acceleration conveyor belt (see diagram on page 78).
Which paper grade is ejected and which continues on is up to the supervisor, who keys in the desired parameters on the system’s touch-screen computer terminal. The operator can choose to do a positive sort (ejecting bright-white paper from everything else) or a negative sort (white paper is passed and everything else is ejected).
Tracking Success
On the break-room wall at the Baltimore plant, there’s a list of the top-10 statements made by paper processors. High on the list is: “I have never had a load of scrap paper rejected.”
While all packers may not be able to make that claim, the Baltimore PaperSort operation can, says Timothy Shifflett, account manager. Since it was installed last year, the system has achieved an average white-paper recovery rate of greater than 90 percent, at a separation purity of about 95 percent, and the plant hasn’t suffered any rejections, he states.
Among its benefits, the system enables processors to extract high-quality grades from mixed paper streams. Thanks to this type of “fiber upgrading,” processors can produce a more valuable package and, thus, increase their revenue—as much as $80 to $90 more a ton than unsorted paper.
PaperSort’s processing speed also enables processors to increase their throughput while, at the same time, reducing the number of employees needed. The Baltimore plant, for instance, can process approximately 2 to 3 tons of office paper an hour—5,000 tons a month—with only one employee, who controls the process via computer. According to MSS, it would take eight to 10 employees to maintain that productivity through hand sorting. Those employees, with salaries and benefits at about $25,000 a year, would cost about $400,000 a year for a two-shift operation.
As Garry Kenny, MSS’s president, asserts, PaperSort “operates more than a magnitude faster than traditional manual paper-grade sorting methods while providing lower labor costs, less variability, and higher quality.”
By not having to hand-sort paper, employees benefit from a safer workplace and an upgrading of their jobs to a higher skill level, says MSS, which claims that any employee can learn how to operate the PaperSort system. “This is a factor that’s not that obvious,” says Kenny. “But when you move workers from being manual sorters to being machine operators or final output inspectors, you change their perception of the job. You change their job status, and you also decrease their exposure to that feed stream.”
Currently, there are only two PaperSort systems in operation—in the Baltimore plant and, more recently, an operation in Germany. Another system is being installed in Denver.
Future enhancements to the technology will focus on the existing sensors and the development of new sensors that can
distinguish groundwood from wood-free paper.
There are also opportunities for PaperSort to be used for jobs other than simply sorting paper. In Europe, for instance, a paper processor is considering using the system to analyze its shredded paper to provide hard data to its mill consumers on the material’s quality. •
Editor’s Note: For more information on PaperSort, contact MSS Inc., 3738 Keystone Ave., Nashville, TN 37211; 615/781-2669 (fax, 615/781-2923); e-mail: magsep@magsep.com; or visit www. magsep.com.
Who’d have thought the scrap paper industry would see the day that a machine could do all the sorting? That day is here.