A significant issue in the operation of the MRF is the choice between mechanical or manual separation techniques. Municipalities today use some of the most innovative solutions when it comes to separation of valuable metals from the mixed waste stream.

By Chris Ramsdel

The business of collecting, processing and recovering valuable material, both ferrous and nonferrous, has spurred a wealth of mixed waste material recovery facilities (MRFs) to install the latest equipment to “mine” for the highest grade product in municipal solid waste (MSW).

A significant issue in the operation of the MRF is the choice between mechanical or manual separation techniques. Older, traditional MRFs rely heavily on manual sorting, which is both expensive and inefficient when handling large volumes of material. Despite the trade-offs between labor and capital costs, most long-term analyses show that automated processing is more cost effective than manual sorting. Automating the sorting process also has the advantages of reducing the health and safety risks that result from workers physically handling materials. That is why many MRFs now employ a total metal recovery system to separate, sort and recover metal. Municipalities today use some of the most innovative solutions when it comes to separation of valuable metals from the mixed waste stream.

Allocating dollars for equipment technology helps local waste recyclers become efficient, low-cost scrap processors since the newer equipment recovers higher levels of marketable grades of metal and plastics, but also saves on energy consumption. Research and development teams at high-tech manufacturers are responsible for many recycling industry product breakthroughs that decrease the cost of sending unrecovered metals and plastics to landfills, recycle valuable materials and generate profits for MRFs around the country. These equipment breakthroughs now maximize recovery—in as small of a footprint as possible—while offering efficiency and safety benefits at the same time.

Technology Turns into Payback

With the latest in magnetic separation equipment, both mixed waste and single stream MRFs can recover nearly 95 percent of the metals passing through their yards instead of sending those metals to the landfill. These facilities save money and enjoy an ongoing revenue stream from metal reclamation by sending less to the landfill.

Technological advancements in separation equipment allow recyclers to recover valuable ferrous and nonferrous metals less than 1-inch (2.54 cm) 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.

Manufacturers work closely with complete systems providers (OEMs) when recommending metal separation equipment. Technicians consider expected capacities, material composition ratios, material size and other variables that factor into the type of equipment needed for any MRF.

The processing and transformation of recyclables into useful material is accomplished starting with various separation equipment within the facility. For example, Suspended Cross-Belt Magnets, Drum Magnets and AIP Magnetic Pulleys are used to recover ferrous metals. An eddy current separator (ECS) is used to recover aluminum cans (UBCs) and other nonferrous metals. Recent eddy current testing at an MRF in Florida showed UBC recovery rates in excess of 99 percent.

Separation Equipment Works in Tandem for Total Recovery

A typical MRF uses a drum feeder to feed material into the system. These facilities then use a series of disc screeners to separate newspaper, cardboard and other papers. The separation continues with a suspended self-cleaning magnet to recover ferrous material, like tin-plated steel cans. The magnet is suspended either cross-belt (perpendicular to the product flow) or inline (parallel) above the product flow.

Self-cleaning magnet systems feature a rubber conveyor belt, bearings, rugged but simple continuous channel frame, adjustable take-ups and shaft-mounted reducer with V-belt coupling to a totally enclosed fan-cooled (TEFC) motor.

Magnetic Pulleys and Magnetic Drum Separators Speed Reclamation

Smaller-sized metal can be recovered downstream with a magnetic pulley, sometimes called a Permanent Magnet Axial Interpole (AIP) Pulley. These pulleys transform a belt conveyor into a powerful self-cleaning magnetic separator.

Ferrous material traveling down the belt conveyor enters the pulley’s magnetic field as it reaches the end of the conveyor. The tramp iron is attracted and held to the belt until it reaches the underside, passes out of the magnetic field and is separately discharged.  Non-magnetic material is discharged over the pulley at its normal trajectory.

Multiple combinations of diameters from 8 to 36 inches and belt widths from 8 to 60 inches are available. MRFs typically use these magnetic pulleys as a secondary ferrous recovery tool when hard-to-separate ferrous materials are involved.

Heavy-duty magnetic drum separators are options for high volume ferrous separation. These powerful magnetic drums feature a non-magnetic exterior shell that is driven around a fixed magnetic element. Ferrous metals are drawn out of the waste stream by the powerful magnetic element and held against the revolving shell. The ferrous metal is released when it reaches a discharge point beyond the magnetic field.

Permanent deep field magnetic drums are found in many MRF operations. Certain models contain Rare Earth permanent magnets and bucking poles to project a deep magnetic field capable of recovering ferrous from distances of up to 15 inches. The drum shell that contacts the ferrous material is made of heavy manganese steel and is abrasion resistant for extending operating life.

Nonferrous Recovery Continues with Eddy Current Separators

The remaining material stream passes over eddy current separators that further separate the nonferrous materials, especially aluminum cans (UBCs). As aluminum cans or other nonferrous metals pass over the drum, the alternating magnetic field creates eddy currents that repel the material away from the conveyor. While other materials drop off at the end of the conveyor, the nonferrous metals are propelled over a splitter for separation.

A most recent addition eddy current separators feature is an eccentric magnetic rotor for separation of nonferrous metals at MRFs. The unit is designed with an eccentrically mounted magnetic rotor within the nonconductive shell. This eccentric rotor concentrates its eddy current forces into a separation zone at the end of the belt. By focusing its field, this design protects the equipment from ferrous material in the flow. The eccentric rotor design reduces long-term wear caused by ferrous build-up.

For coarse materials greater than 1 inch, this unit provides excellent separation with a deep field rotor designed for maximum trajectory. For nonferrous fines measuring less than one inch, a unit with high-frequency rotor configuration concentrates the eddy currents closer to the belt’s surface, improving separation of this difficult material.

Also part of MRF operations are vibratory feeders and sensor sorting equipment. Brute force feeders and electromagnetic feeders, with their heavy-duty construction, are recommended for multiple applications.

Brute force feeders provide a cost-effective means to feed or screen large volumes of solid waste material where limited minimum feed rate adjustability is required. These units are incredibly fast, durable and reliable. They operate quietly and efficiently. Multiple sizes are available and trays can be customized to satisfy customers’ specific requirements. Brute force feeders are an ideal choice for spreading materials across the working width of separation equipment.

Last Chance Monitoring

In spite of the improvement in recovery, MRF operators still know intuitively that they continue to miss metal as they watch potential profits go to the landfill. That is where some waste recycling operations should consider installing a Metal Loss Monitor (MLM) to help confirm those losses. This is typically positioned on the final waste stream in these facilities and continually scans the residue stream for metal that has escaped the process and 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. 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 properly evaluate whether additional or different separators should be used to reduce metal losses.

The type of recycling equipment mentioned previously allows MSW/MRF facilities to recover valuable ferrous and nonferrous materials previously earmarked for landfills. The use of eddy current separators, drum magnet separators and even the Metal Loss Monitor helps increase the bottom line and keep valuable metals, plastics and more out of the waste stream. Manufacturers of this type of recycling equipment continue to invest in new technologies to further extract materials from comingled waste.

Chris Ramsdell is Product Manager—Recycling Equipment at Eriez (Erie, PA). He can be reached at (814) 835-6000 or via e-mail at [email protected]. For more information, visit www.eriez.com.

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