A fundamental component

In the past decade, the purchasing and disposal habits of U.S. consumers have taken many turns. With these changes, which have been exacerbated by the coronavirus pandemic, the material recovery facilities (MRFs) that manage this material at the end of its life have had to adapt. Most recently, a growing preference for online consumerism and a rise in the use of plastic film have been especially disruptive. These changes, paired with an increasingly strained labor market, have forced MRFs across the country to find innovative solutions to maintain successful operations.

“There used to be a lot more paper and a lot less contamination,” says Ashley Davis, sales and marketing director for San Diego-based CP Group, of the recycling stream. “Most of the 2D material was fiber—[typically] newspaper—and containers were 3D and rigid. Screens used to be the primary method to sort paper from containers, or 2D from 3D.”

Plastic film and contamination have increased in the last decade, she adds.

“Online consumerism, or the ‘Amazon effect,’ has also happened, so there is a lot more cardboard, including smaller 3D boxes,” Davis says.

To manage contamination and the increase in boxes, she says primary screens have been redeveloped to be more robust and wrap-resistant.

Mark Neitzey, national sales director at Norwalk, Connecticut-based Van Dyk Recycling Solutions, previously told Recycling Today, a sister publication of Waste Today, “Screens are like the heart and lungs” of a sorting system. Given their integral role, their efficiency greatly affects a system’s overall performance.

Meeting new demands

The primary function of screens has shifted in recent years “to properly feed downstream automation by liberating conjoined materials and making the fractions more homogeneous, so that the optical sorters [can] do a better job sorting commodities,” Davis says.

CP Group offers its CP Auger Screen as an anti-wrapping screening solution. The technology is used to fractionate inbound material streams and eliminate the need for presorting, according to the company.

Van Dyk also has offered several anti-wrapping screens over the last decade, each suited to different applications with various shaft sizes, star shapes and spacing to accommodate each plant’s material.

Bulk Handling Systems (BHS), a systems provider and manufacturer based in Eugene, Oregon, has experimented with its own screening development— the Tri-Disc.

Chris Parr, BHS director of sales and application engineering, says, “There’s a larger tri and a smaller tri, and they actually create a very exact opening between the sets of shafts that allows very precise sizing.”

These applications include 2D and 3D separation, fiber cleanup, glass breaking and fines removal.

Machinex Industries Inc., Quebec, which designs and manufactures recycling sorting systems, considers the mass balance of the system and ensures each stream is handled appropriately.

Chris Hawn, CEO of Machinex Technologies, the company’s U.S. division that is based in North Carolina, says, “The front end of the sorting process is an area where technology has improved. As such, in today’s environment of recovery and purity, utilizing technology to divide the stream into streams that can be processed with the correct downstream sorting technologies is essential in both improving efficiency and minimizing labor.”

Hawn says a possible solution is the use of trommel screens. “The age-old technology offers the benefits of being solidly built machine[s] that give you the capability, within a single unit, of making multiple cuts of material in a small footprint.”

He adds, “The secret sauce ... of recycling is once you’ve separated various streams, you never blend them back together. Each stream should go to the next appropriate secondary treatment process.

“The use of a trommel, with multiple cuts, makes sure an appropriate flow of material is seeing the equipment that is designed to optimize separation.”

Hawn says a ballistic or optical sorter, for example, operates best when the infeed material is uniform in size and flow, resulting in premium efficiency of the specific machine.

“Every manufacturer recognizes each piece of the separation puzzle is efficient with specific material,” he says, adding that Machinex focuses on the process rather than a specific piece of machinery.

Lifting the burden

Relying on manual labor for presorting can present challenges for MRF operators, including ensuring personnel safety.

“One thing that came out [of the pandemic] is we cannot be so dependent on labor,” Neitzey says. “It’s not just that labor is expensive, but we could not predict who’s going to show up for work.”

He adds that a presorter is “the first person that sees the material as it comes up the conveyor belt.” To better protect these workers or shift them into other roles, Neitzey says it’s integral to implement material prep earlier in a system.

For front-end screening, Van Dyk offers the Günther Splitter screen—a nonwrapping, self-cleaning spiral screen. Personnel safety also is a key design factor for CP’s auger screen, which Davis says drastically has reduced the need for manual sorters on recent installations.

“By fractionating material at the infeed of the system—prior to people—less people are needed to sort out large contamination, rigids and metals, since 60 percent of the inbound material bypasses these people,” she says. “Their visibility is much better, the burden depth is decreased, and they can do their job safely without having to hit the pause button as much.”

Using an auger screen, Davis recalls systems where only two to four people were needed for a postscreening sort, rather than the typical eight to 10 people.

Hawn says trommel screens are “reducing headcount and keeping capacities on and leveling up the flow.”

He adds, “[I]t’s no criticism against the auger screens because they can be used in a similar fashion to trommels—they’ve got their place in the world—but we also feel a trommel does a very good job and lends itself to potentially doing more sizing in a tighter space.”

Permanent fixture

As the adoption of optical sorters and robots continues, the use of screens has become increasingly important. For automation to work most efficiently, Davis says the equipment must be properly fed.

“Material needs to be singulated and sized appropriately, and screens play a key role in that,” she says.

The key to success, Hawn says, is to present these devices with a consistent monolayer of material so commodities are easily identifiable.

By prescreening residuals and fines, Parr says opticals can be more efficient.

“Screens are important because they handle high volumes of material,” he says. “We have screens that handle 60-plus tons per hour; there’s no optical or robotic piece of equipment in the world that can handle that kind of tonnage.”

Though MRF equipment has changed over the years, Davis says screens are here to stay. “Screens are needed to split the material into more manageable and homogeneous streams and properly feed downstream automation,” she says. “Optical sorters and robots simply cannot take the volume of material that screens can.”

“The screen is the best way to agitate and break up the material as well as … divide the material into multiple lines,” Parr says. “For example, if you have 30 tons an hour coming in, and your opticals can handle … 8 tons an hour apiece, you need to split it into four lines. As you agitate the material with a screen and get it broken up and moving, you can divide it much easier because it’s more fluid.”

This article previously appeared in the March issue of Recycling Today, a sister publication to Waste Today. The author can be reached at hrischar@gie.net.