Screening basics

Screening technology used in North American recycling systems has remained largely unchanged for the past 25 years; but, more recently, recycling equipment manufacturers have introduced new technologies designed to optimize North American material recovery facilities (MRFs).

MRF operators are taking advantage of these developments, installing updated screens on the front end of their sorting systems to ensure that recovered material is high quality and that day-to-day operations are as efficient and profitable as possible.

Suppliers of screening technology say operators can take several steps to achieve better performance from their legacy screens, including budgeting to replace older screens and keeping up with cleaning and preventive maintenance.

“Screens have evolved,” says John Kemp, sales engineer and operations manager at CP Group, San Diego. “Now, we have the anti-wrapping screen. When I first started at CP Manufacturing, it was an entirely different disc.”

Mark Neitzey, national sales director at Van Dyk Recycling Solutions (VDRS), Norwalk, Connecticut, says, “Screens are like the heart and lungs” of a sorting system. “If they’re not taken care of properly, your system isn’t going to perform.”

Keep ’em clean

To prevent traditional disc screens from clogging and causing downtime, operators should have a cleaning program in place to remove plastic film from the discs’ shafts. Cleaning the screen is time- and labor-intensive, so Neitzey suggests the maintenance and operations teams, as well as an outside cleaning crew, share this responsibility. The task also carries a safety risk, so all team members should be properly trained.

Plessisville, Quebec-based Machinex Project Director Sébastien Roy says best practices for screen maintenance include removing wrapped or jammed material from the shafts and discs and inspecting the discs for wear.

Photo provided by Van Dyk Recycling Solutions

Kemp says replacing discs on a regular interval improves the life of the screen and the quality of the sorted recyclables. For example, the CP screen requires disc changes roughly every 2,000 hours, and CP’s anti-wrap screen requires disc changes roughly every 3,000 hours. CP also uses steel on its old corrugated containers (OCC) screen to reduce the need for disc changes.

“A lot of screen maintenance is putting good money into bad,” Kemp says. “If you change the discs, you can run longer and maintain a better product consistently.”

Neitzey says in his experience most customers go six months without changing discs, and “that’s when you can run into problems.” He advises that the maintenance team inspect sprockets, bearings, belts and chains and adjust them as needed during disc rotation to make the best use of downtime.

Invest in anti-wrapping

In an average 35-ton-per-hour system, more than 100,000 plastic bags enter the system per hour, according to VDRS.

As a result, the plastic film wraps around the discs and blocks openings in the screen, reducing separation efficacy and opening the door to contamination, Roy says.

Photo provided by Van Dyk Recycling Solutions

Suppliers to MRF operators have developed nonwrapping or anti-wrap screens designed to combat the plastic bag “epidemic” and help reduce downtime and maintenance associated with plastic film, Neitzey says. The screens feature rotor shafts with a larger diameter, which make wrapping more difficult.

For its anti-wrapping screen, CP Group developed an egg-shaped disc, “which is aggressive enough to pull out today’s type of material,” Kemp says.

Investing in nonwrapping screens will help MRF operators reduce their screen maintenance costs and downtime, he adds.

Neitzey says, “If you’ve got the old style [screen], it’s time to look at anti-wrapping [screens] and a ballistic separator. While you’re waiting for that to come online, have a good program on cleaning and star changing and do predictive maintenance before the screen fails,” he adds.

Enhance the front end

A traditional recycling system in the U.S. includes OCC, mixed paper, container and polishing screens, says Mat Everhart, CEO of Stadler America, Colfax, North Carolina. But ballistic separators commonly have been used to separate 3D materials from 2D materials in Europe.

VDRS offers an elliptical separator—its version of a ballistic separator—while Machinex, CP Group and Stadler offer ballistic separators, all of which feature paddles rather than discs.

Employing one of these separators to sort 3D material from 2D material “is a potential solution to solving your screen problems,” Neitzey says.

While MRFs are becoming increasingly automated, many still rely on laborers to presort material before it arrives to the screens. However, some technology that systems integrators have introduced can help to reduce manual presorting. For example, CP Group offers its auger screen, which sizes material by using a series of cantilevered augers that mitigates wrapping and jamming and reduces manual sorters. “The CP auger screen is a primary screen, which eliminates the presort,” Kemp says. “On the postsort, less humans are needed because over 65 percent of the material is diverted to the next phases of screening, including all the harmful objects, such as sharps and fines.”

Move toward automation

As equipment and technology advance, MRFs are moving toward highly automated or fully automated recycling systems that could help to reduce labor costs.

Stadler helps operators achieve automation with its screening drum, which does “all of the jobs” of the different screens with one screen, Everhart says. By using better screening equipment on the front end, MRFs have been able to reduce labor on the quality control line by 75 percent or more in some cases, Everhart says.

“If you look at a Stadler system on paper, it looks a lot different in layout from an American system largely because the European community went away from commingled recyclables 15 years ago. When they did, the industry evolved in a different direction,” Everhart says. “This is the direction the American stream is going to now, with more film and flexible packaging and a lot less newspaper and larger plastics.”

Ask the manufacturer

Training operators on proper screen maintenance and cleaning is important to get the best performance out of the system.

“We train an operator on how the screen works, how it should be serviced and the interval, and then they move on, and someone comes in with no experience and the manuals are gone,” Neitzey says.

When this happens, a MRF operator should contact the manufacturer of the screen, he says, to ask for a new manual or a training guide.

“It happens so often,” he says. “We train someone, they move on, and you’re trying to start from scratch. Consult your manufacturer. If you don’t have the manual, ask for a new copy to try to get some continuity in your operation.”

The author is the digital editor for the Recycling Today Media Group and can be contacted at kmaile@gie.net.