What’s the driving force behind screen innovation? According to Mark Henke, recycling manager at Phoenix-based Republic Services, throughput demands are a driving force behind innovations in screening technologies designed for material recovery facilities (MRFs).
“We’re always wanting to go faster, produce more, do things quicker and with less labor,” he said during a presentation on screens and ballistic separators during the MRF Operations Forum in October 2020.
He added that labor costs are another driving force behind screening innovations.
“Many states are moving through minimum wage increases,” Henke said. “Another piece is labor shortage. Where are we getting our labor and why are we having a hard time finding labor.”
Packaging design changes have also prompted screening innovations. With the pandemic, more people are ordering online and, as a result, more packaging is ending up in homes and residential recycling systems. So, he said, the materials being screened at MRFs is changing over time.
MRF operators have several options to screen materials, including traditional screens, nonwrap screens, elliptical screens and optical sorters. During the MRF Operations Forum, Henke discussed the advantages of each of those screen types.
Traditional screens
Over time, traditional screens tend to lose efficiency if the stars get tangled with materials, which impacts both quality and production. Henke said MRF operators using traditional screens can combat the loss of efficiency by adjusting screen angles and speeds to prevent wrapping. He added that MRF operators running traditional screens need to spend extra maintenance time cleaning out screens regularly.
Nonwrap screens
Nonwrap screens feature wider diameter shafts that feature wide screens that exceed 10 to 12 feet depending on the specific screen design, Henke said. He added that MRF operators using nonwrap screens can increase throughput compared with using traditional screens since the throughput will stay more consistent throughout the day. Maintenance on nonwrap screens are simpler than with traditional screens, and this design helps to extend the life of stars.
However, he said, one downside to nonwrap screens is that some objects that would be tanglers on traditional screens could end up migrating downstream, causing a drop in efficiency levels. Additionally, shafts are a bit more expensive to replace with this design.
Elliptical screens
Henke said ellipticals are “a good alternative” to traditional and nonwrap screen applications. Ellipticals can feature various sizes to allow for a MRF operator’s desired throughput. He said the agitation with this model of screening performs good fiber and container separation that can produce three streams—some materials will go over the top of the screen—such as lighter materials like paper—while containers may bounce backward to another stream and then smaller materials such as glass can fall through holes in the elliptical. He said this model reduces downstream labor and quality control efforts.
Maintenance and daily cleaning requirements are minimal with this style of screening, too. Paddles on this model of screen can last about five years.
Optical sorters
When using optical sorters, MRF operators can achieve pretty good throughput levels, depending on the width of the conveyors. With opticals, Henke said high-speed conveyors will typically run anywhere from 200 to 300 feet per minute.
He also noted that these machines feature infrared detection and cameras that allow for 97 to 98 percent accuracy and purity with sorting. “98 percent accuracy means what that particular unit is targeting is actually being recognized and hit on with air ejection nozzles, and purity is what it collects in your bunker,” he said. “This means reduced labor downstream.”
When maintaining optical sorters, MRF operators need to clean and calibrate the machines regularly.
“Over time, the lines of calibration will drift in which it may not be as accurate as it was when it was set,” Henke said.
As far as cleaning, he said operators need to focus on keeping lenses and air nozzles clean. In MRFs that may experience freezing temperatures, he said operators might want to consider having an air dryer on the system to ensure nozzles won’t develop moisture and freeze in the winter.
View Henke's session from the MRF Operations Forum broadcast event below.