Equipment Focus: Paper Sorting

Oct 4, 2018, 19:01 PM
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September/October 2018

By Ken McEntee

Paper-SortingIn recent years, Waste Management (Houston), the world’s largest operator of material recovery facilities, has invited equipment vendors to discuss their latest technologies for processing recyclable commodities at an annual summit. “At first it was all about how we could become more efficient at processing material. Then the focus became how we could potentially cut back on labor dollars, which is a big expense for us,” says Brent Bell, president of Waste Management’s Recycle America division. “During the past nine to 12 months, we’ve been asking how we can make cleaner, higher-quality material as opposed to just being efficient. Today, you have to make quality material, or you can’t move it.”

Motivating this focus on quality, in large part, are changes over the past year in China’s scrap import regulations. In July 2017, the Chinese government notified the World Trade Organization of its intention to ban imports of mixed paper and some other recyclables in early 2018. It followed that bombshell with the announcement that for most scrap imports it did not ban, contaminants could not exceed 0.5 percent—a standard many consider unattainable, particularly by single-stream residential MRFs.

For MRFs accustomed to exporting their mixed paper to China, the announcement sparked intense interest in the latest paper sorting equipment, particularly optical sorting systems. “We’re backlogged,” says the North American sales manager for a Quebec-based manufacturer of sorting machinery. While the company is doing fewer new turnkey MRF installations, “we are doing more of these systems than we have ever seen on the upgrade side. … People who are serious in the game are all looking at options to upgrade their existing plants.”

The sales director for a Nashville-based manufacturer of optical sorting technology says interest in its products actually started to accelerate before the Chinese announcements. “It started to pick up about 18 months ago, after the opening of the Republic Waste (70 ton-per-hour) facility in Las Vegas,” he says, which the company was able to showcase through tours it offered during that year’s Waste Expo convention. “Then once the market started changing last fall, all of a sudden people started to say, ‘Hey, we need to do something.’ It’s been totally crazy since then.” In April, this company reported that it was in the process of supplying 29 optical sorter units for paper separation to 13 customers across North America, and more units were on order. It says each unit can replace up to 20 human sorters and can make more than 1,000 picks per minute, compared with 40 to 45 picks per minute for a human sorter.

MRFs have used optical sorting and cleaning for 20 to 25 years on their container lines, the North American sales manager says, but the technology has been less common on paper lines, where processors did not consider that level of separation necessary to produce a salable product. That’s changing, however. “I wouldn’t overdramatize [the situation to say] that every MRF out there is now doing optical sort on the fiber line,” says Nathiel Egosi, president and CEO of RRT Design & Construction (Melville, N.Y.). “But I would say that every MRF that isn’t doing it now is at least evaluating it.”

With new optical sorting technologies now available, as well as other new tools for separating paper out of a residential stream, here’s an overview of how equipment could help MRFs and other processing facilities achieve higher quality.

Starting with screens

A MRF’s paper sorting operation aims to pull clean OCC, ONP, white paper, or even mixed paper out of a cornucopia of received recyclables. The process often begins with the separation of large sections of old corrugated from the rest of the paper and containers. OCC screens have spinning shafts that contain disks or “stars.” Sheets or sections of rigid OCC move over the disks and get deposited onto a belt. Smaller pieces of paper and other pliable materials fall through the disks onto another conveyor, which transports the fiber to additional screens to remove food and beverage containers.

The biggest limitation with OCC and paper screens is the fact that plastic film and cordage can wrap around the shafts, which restricts their effectiveness and requires frequent cleaning. The tangled plastic around the shafts can “turn the screens into conveyors,” explains the Midwest sales manager for a Connecticut manufacturer. “The separation of containers from paper just declines as the shift goes along,” he says. “Typically, it takes one to four people, depending on how many screens you have, upwards of three or four hours to clean the screens.”

Manufacturers of these screens are moving to larger-diameter shafts that are harder for bags and film to wrap around, Egosi says. Indeed, the Midwest sales manager says his company’s Michigan-based sister company recently developed a nonwrapping, angled disk screen: “a larger-shaft screen, with larger-diameter shafts and stars that essentially eliminates the wrapping of all plastic bags. We have those installed in about a dozen plants, and that’s the only screen that we will continue to use in the future.”

The paper and other materials that fall through the OCC screen might move on to a glass-breaking and separation system and/or a manual sorting line before entering an ONP screen. That screen recovers the old newspaper, separates and collects plastic and other containers, and sometimes separates and collects mixed paper.

Going ballistic

More recently, MRFs have started using ballistic separators instead of screens for separating newspaper and other fiber from containers after the OCC screens, Egosi says. “Ballistic separators separate items into ‘2-D’ versus 3-D items, such as flat, two-dimensional sheets of paper compared to a three-dimensional bottle.”

Instead of having rotating shafts, ballistic separators have inclined rows of paddles that alternately move up and down—Egosi compares them to the pedals of an elliptical exercise machine. The 3-D containers moving up the incline bounce up, back, and off the machine for collection. Paper continues to move up the paddles and drops off the top. Smaller fines drop through the paddles for collection below.

Ballistic separators eliminate the problem of plastic film wrapping around the screen shafts. And “ballistics don’t have any wear issues because there are no disks to wear out,” Egosi says. But they have disadvantages as well. Today’s lighter-weight PET bottles and aluminum cans can be so tightly compacted that they are essentially flat, the North American sales manager says, and they can travel with paper to the end of the paddles. Also, Egosi says, “the throughput capacity is much lower than the screen,” in part because fiber must move across a ballistic separator in a single layer.

“Once you get more than one layer of fiber, almost all separation becomes ineffective,” he says. “So the remedy is to just have the machine to be wider to spread the material out.” Of course, there are limitations on how wide a machine can be, he notes, “so another remedy is to stack one machine above the other.” In the end, the throughput of a single screen can be double that of a ballistic separator, Egosi says, so many MRFs use a screen for the initial major separation followed by a ballistic separator for final polishing or cleanup.

The Quebec company representative disagrees with Egosi’s assessment of ballistic separators’ throughput capacity. “Replacing star screens with an equal amount of ballistic separators will maintain the same throughput capacity with more uptime because of the reduced wrapping and cleaning” the ballistic separators require, he says.

Another, less common option for paper sorting in a MRF is a trommel screen. “Trommel screens work similarly to paper screens or ballistic separators,” Egosi says. “The benefit of the trommel screen is there is substantially more agitation and separation, so material can be separated based on particle size.” Although they were popular in mixed fiber separating plants in the 1990s, they’ve fallen out of favor, in part because they take up a lot of space, create a lot of dust, and most MRF equipment manufacturers don’t make them, he notes. “Time will tell” whether MRF customers will return to this technology, he says.

New optical sorting options

After the screening or ballistic separation machines, optical sorters remove any remaining nonfiber items and separate different types of fiber, Egosi says. Near-infrared, or NIR, detection has been the most common technology for optical sorting in MRFs to date, but new technologies are emerging to supplement or replace NIR, these sources say.

The Quebec-based company is using a hyperspectral camera along with NIR identification, the North American sales manager says. “The hyperspectral camera provides the entire wave form to identify the object you want to blow off the belt,” he explains. “With NIR, you may be able to notice 16 [to] 256 points on an object. The hyperspectral [camera] gives you the entire curves without a chance of missing valuable information.”

A Norwegian company with North American headquarters in West Sacramento, Calif., introduced a new laser object detection system this year. “NIR scans the conveyor and can tell exactly what kind of material is on the conveyor. [With LOD], we can see the three-dimensional materials that we cannot see with the NIR, such as black plastics and other black items,” says the company’s regional director for the Americas. NIR and LOD can be used in tandem, he says.

An Oregon company’s technology uses high-resolution RGB color-detection cameras to identify OCC and multicolored boxboard, which it positively sorts off the belt, says the company’s vice president of sales and marketing. The technology “identifies brown grades and multicolored boxboard at a rate of 15 million pixels per second versus the 120,000 pixels per second that NIR detection offers,” he says. “This makes a clear distinction between fiber types, and by employing it, we deliver a clean news stream and a highly pure OCC product.”

Positive developments

As that vice president notes, another change manufacturers and MRF operators are making with optical sortation is performing positive sorting instead of negative sorting. In negative sorting, air jets blow unwanted material off the sorting belt, allowing the desired material to remain on the conveyor. Positive sorting is the opposite: The air jets remove the desired fiber types and leave the contaminants on the belt.

Positive sorting is “a different approach from what most people are doing,” explains the Midwest sales manager for the Connecticut company. In negative sorting, “people are trying to shoot the contamination out of their paper products … but some contamination is still going to get through,” he says. “By positively removing the materials we want to recover, what comes off the belt is completely clean.”

In his company’s systems, the materials that remain on the belt, such as bottles, cans, and remaining paper, go to another sorting line. “[We’re] installing a ballistic separator after the optical sort to do a final separation of the containers from plastic film,” he says. “Then we can recover the film as either a product or [to send] to residue.” One MRF in San Diego is using this approach, and another installation is in progress at a Texas facility, he says.

The Quebec-based company is taking a slightly different approach, combining positive and negative sorting into a “dual-eject” system. Its optical sorters blow contaminants off the belt in one direction, while shooting brown grades off in the other. The problem this solves, the North American sales manager says, is capturing small pieces of OCC, which are abundant in residential pickups from online shopping deliveries—what he calls the “Amazon effect.” As much as 40 percent of the OCC and boxboard that comes into a MRF may be getting past the OCC screen because of its smaller size, he says. That material ends up in the stream with containers and other nonfiber contaminants, “then [workers] are hand-sorting the browns. That’s a lot of hand-picking to try to capture that OCC.”

The dual-eject system, along with adjustments at the OCC screen, allow the capture of a higher volume of clean OCC, the North American sales manager says. “We’re trying to get everything 12 inches or larger at the screen, then get the minus-12 [inches] at the optical sorters. … We recently installed a system in Chicago that included this dual-eject optical sort off of the news screen, and it resulted in a significant increase in [salable] OCC. Before, they had six people on a manual sorting line, and [now] they are down to two.”

One emerging technology is robotic picking arms paired with optical sortation. Robotics is too new and untested to make a significant impact on paper sorting today, Egosi says, but Waste Management installed its first robotic sorters for testing in a Texas facility last year, Bell says. “We’re looking for that to be another method to clean the material,” he says. “We’re working with a vendor in doing research and development on it. It’s performing well enough that we are potentially looking for additional installations. I think robotics has a lot of upside to it, and I’m pretty optimistic about the future for robotics in our recycling facilities.” (For more on robotics, see “Robot-Assisted Sorting” in the Equipment and Services section of Scrap’s July/August issue.)

Considering an upgrade?

Operators that want to add optical sorters or other new technology to an existing MRF might face a challenge, the North American sales manager says. “It’s a space-configuration and flow-configuration issue. You want to make sure that you give as much accessibility [as possible] to the machines for maintenance purposes and for cleaning and everything like that. In a perfect world, you have space so we can install these, but that doesn’t happen as often as we want.” At one facility, he says, “the distance between the news screen and the ballistic separator was enough that we were able to move the news screen back and get the optical sorter between the two. But often you have to add more transfer conveyors to be able to get it to work.”

The Norwegian company representative notes, however, that not all equipment requires additional space. Its laser system mounts to the same platform as the existing sorting equipment, so it does not require an additional circuit or floor space, he says.

Egosi points out that these new technologies are different dimensions than their predecessors. “The shaft diameter of the paper screens is getting to be larger diameter so things don’t wrap around on the screens,” he says. “The ballistic separators are also getting wider to provide a greater throughput. So the optical sorter also has to be wider so the material stays spread out and more easily detectable.” Such equipment likely requires more space, new conveyors, more compressed air, more electrical power, more service platforms, “and, of course, much higher level of training and skill sets by plant mechanics,” he says. Even so, as the technology increases in sophistication, “the MRFs are becoming more dependent on manufacturers for service versus doing it themselves.”

And then there’s the cost. These sources cite prices from $200,000 to $1 million for optical sorting technology, depending on the width and number and type of sensors. Including necessary plant modifications and supporting equipment, the price tag could approach $2 million, Egosi says.

“People considering the improvement have to determine whether they’re ready to spend more capital per ton to [produce] a higher quality product,” says the sales director for the Nashville-based company. “A lot of facilities are slowing down their lines so that the quality is better coming out in the back. That also increases the processing and operating costs. If you want to still stay at the same volume you’re doing, you may need to buy more equipment to get you to the quality you’re aiming for.”

Can these advancements in paper sorting equipment create paper bales with less than 0.5 percent prohibitives, as China now requires? It depends on the quality of the material coming into the MRF, these sources say. “We’re putting junk into the system, and we’re expecting to make beautifully clean material,” the Midwest sales manager says. “If we didn’t have the plastic bags and other junk getting into the system, we would have no issue just using screens again to make China quality material. You wouldn’t have to invest in expensive optical sorting and retrofits.”

The North American sales manager for the Quebec company says the 0.5 percent spec is “tight.” He notes that “on a positive eject of fiber, you have a better chance of meeting that 0.5 percent, but your yield loss of good fiber downstream is going to be enormous.”

“The technology we have today absolutely will significantly reduce the contamination in paper” to produce good, ISRI specification-grade material, he says. “That wasn’t true 18 years ago.”

Ken McEntee is publisher and editor of The Paper Stock Report,

China’s import policy changes have closed off some markets for recovered fiber and raised the quality requirements of others. A variety of new separation technologies are offering MRFs hope that they can achieve cleaner fiber streams.
  • 2018
  • Sep_Oct

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