Making MRFs More Efficient

There are two things on the minds of MRF operators, according to Scott Jable, director of North American sales for Stadler America LLC: labor reduction and material cleanliness. “Both are helped by automation,” he says.

While those are important concerns, Tony Bonds, marketing manager, CP Group, lists ­additional challenges for today’s MRFs:

• A more complex and more contaminated input stream (light-weighting of all packaging materials, the “Amazon” effect [increased amounts of cardboard and packing materials], flexible plastic packaging)
• Higher purity requirements for commodities across the board from end markets (China’s Green Fence, which cut export volume of mixed plastics by 40%, and National Sword—considered the second Green Fence—which cut export volume of mixed plastics another 40%)
• Higher cost of and difficulty in recruiting and retaining personnel—manual sorters, in particular
• Ability to process more volume
• Ability to process materials from different sources
• Need for lower-maintenance equipment
• Need for highly integrated controls
  with smart sensors and feedback to the plant operator

Sorting it Out
Mechanical sorting is already taking over from manual, states Gary Brooks, director of sales—recycling solutions, Marathon Equipment Co. “We’ve migrated to conveyor-fed [from manual].” All the conveyors they build are one-offs; there are no cookie-cutter conveyors because the setup depends on the MRFs, the footprint, and how they load—over the rear or over the side.

Belt-type conveyors are the most common, but AirTrim has completed several projects with pneumatic conveyors. It’s most successful with lighter materials such as plastics and aluminum cans, says Mike Stradiot, vice president of marketing and sales. “A pneumatic system is [al]most always more expensive to install, but once in place, the maintenance is a fraction of the standard and industry-accepted belt conveyors.”

Once the material has been loaded onto the conveyor, it must be separated. “You need metal separators,” says Roland Zimmer, CEO, Zimmer American Recycling Solutions, noting that aluminum is the most-recycled metal.

Vibrating screens and gravity separators ­assist in this process, feeding material onto magnetic separation equipment and onto conveyor belts. An Eddy Current Separator is another option to separate aluminum cans or other nonferrous metals. A recent test at a MRF in Florida showed an ECS recovery rate in excess of 99% for used beverage cans.

Technological advancements in separation equipment can now recover valuable ferrous and nonferrous metals less than 1 inch in diameter from the fines waste stream. That means reducing the amount of waste slated for the landfill and reclaiming thousands of pounds of metal each day.

In spite of the improved efficiency in ­recovery, MRF operators still know intuitively that they continue to miss metal. Some waste recycling operations have installed the Metal Loss Monitor to help confirm those losses. Typically positioned on the final waste stream, the MLM continually scans the residue stream for metal that has escaped the process and is headed for landfill disposal.

“The MLM takes the guesswork out of metal recovery, giving users the ability to observe the performance of their systems for variations over time,” states Chris Ramsdell, Eriez product manager, recycling equipment. With the MLM in place, maintenance issues and adjustment requirements are quickly spotted when losses spike. The data gathered also offers beneficial insight needed to evaluate whether additional or different separators should be used to reduce metal losses.

A low-profile Eddy Current Separator from Eriez is 20 inches high, which allows systems providers to “shoehorn” the equipment into areas with limited vertical space, Ramsdell says. “Our focus at Eriez is to maximize recovery in as small a footprint as possible, offering efficiency and safety benefits as well.” For example, special side guides prevent the possibility of someone falling onto the conveyor.

Plastics are the next step, Zimmer contends. “The typical MRF concentrates on metal, paper, cardboard, plastic, but there has been a change. There are different material streams today.” The shift in MRFs from paper to plastics is changing configurations and equipment.

Plastic Surgery
Some of the fastest-growing and most challenging commodities are flexible plastic packaging and film bags. Although the UK is moving toward banning plastic bags after seeing a significant decrease since imposing a charge on them, the US is not following suit, so they have to be dealt with here.

Over the last two years, Bonds says, MSS Inc. has worked with industry groups and projects to test and optimize the CIRRUS ­FiberMax technology to mechanically handle, optically identify, and physically sort FPP from newspaper or mixed paper streams. The ultra-low weight of FPP makes it a difficult material in several areas of a MRF. “The FiberMax has made great strides towards higher FPP recovery with minimum fiber cross-contamination.”

Recovery methods also include the use of electromagnetic feeders to help meter plastic regrind and heavy-duty feeders to spread and separate materials to sorters. This equipment is typically installed with other OEM systems at MRFs, Eriez’s Ramsdell explains. Maximizing recovery in as small a footprint as possible can decrease the amount of unrecovered metals and plastics sent to landfills, leading to profits for MRFs through recycling and improved efficiency.

Efficiency can be improved with a range of technologies, says Bernhard Gabauer, plastic specialist for Bühler. “There is no single feature or component that defines the overall performance of any sorter. So, for example, if you improve signal processing, you will improve the efficiency; if you have a better feed system, higher quality inspection, and/or accurate rejection systems, you will improve efficiency.” Their technology can accurately separate valuable plastics from mixed waste, even if the contamination levels vary.

The mixed plastic stream includes numbers 1–7, but Zimmer explains that it’s necessary to eliminate PVC for waste-to-energy systems. PET and polypropylene “go through optical sorting, get washed and repalletized for reuse.”

Optical Illusion
Optical sorting is evolving. As it does, the way we define efficiency in sorting is, too. “Originally, it was focused on how well a sorter cleaned a flow of product,” says Gabauer. “Now, with many solutions able to provide a ‘good enough’ clean, the term efficiency involves losing the least amount of good product with the rejected product.”

Because there is more demand for ­upgrading plastic recycling—and more value in it—Zimmer says plastics recyclers sort mixed plastic bale using optical sorters or camera- or infrared-based sorters. “Optical sorting is growing because it provides a cleaner product.”

In order to meet quality requirements, we not only have to be able to detect and remove challenging materials (such as contaminants that look the same or are the same color as the good material, such as clear PVC from Clear PET), we must also deliver the highest yield, or the highest reject concentration.

Bühler has a fully integrated optical sorting station so that processors in the plastics recycling industry don’t have to source separate elements from multiple suppliers and can obtain a highly efficient and innovative plastic processing line from one supplier.

The CIRRUS FiberMax optical sorter from the CP Group is used to remove prohibitives and outthrows from newspaper and mixed paper. Other benefits it offers include:

• Full NIR and color identification capabilities for all materials in a MRF stream
• Eliminates up to 20 manual sorters
• Improves fiber purity and recovers flat containers
• Easily integrates into existing facilities
• Provides quick return on investment
• Low maintenance with automated internal calibration

A FiberMax unit can average about 800 picks per minute, the equivalent of 15–20 manual sorters. It processes contaminated fiber streams at 1,000 FPM, which is twice as fast as conventional optical sorters. This allows it to handle higher volumes over the same machine width and, on average, offer a lower belt coverage in the sensing zone, which reduces the collateral damage of fiber being ejected with the contaminants.

The CIRRUS PlasticMax also offers full NIR and color identification, which allows the optical sorters to specify what material should be sorted vs. relying on physical characteristics such as density, size, or shape. This feature offers an advantage for sorting complex input streams because sensitivity settings in the software can be applied to specific commodities to achieve final product purity requirements more easily.

Optical sorters offer more consistent and higher quality than manual sort lines. As Bonds says, they never get sick or have a bad day. MaxSelect utilizes patented sequential scanning for the highest-definition scan.

Screening Processes go Ballistic
Managing and treating the less than 2-inch glass fines fractions in MRFs has become progressively more difficult and expensive as the levels of contamination have been increasing. The low intrinsic value of glass in most markets makes any significant capital investment difficult to justify. “New MRFs include a glass cleanup system,” observes Jable, because they need less than 10% non-glass recyclable NGR. “You send 1 1/2 minus material (broken glass) over the flip-flop screen or zig-zag screen. It falls, then you shoot air up to blow out the lights. From there, it could go to an optical sorter or to strategic materials.”

This system can be retrofitted, but a high volume of material is necessary for a good return. There are more options with a new MRF, Jable continues. “You can use a 3D trommel and ballistic separator now; they were not available even five years ago.”

Something else not available five years ago is CP Group’s latest generation air drum separator, LightsOut. This air separation solution cleans mixed broken glass generated from MRFs. Compared with other glass cleaning systems, it has lower operating costs, partly due to the fact that it requires virtually no maintenance, doesn’t jam, and has no wear parts. Operating at low air pressures and without the need for an expensive baghouse or cyclone system, the LightsOut provides a high degree of separation with little effort and noise.