How modern separation equipment is increasing metal recovery rates at MRFs

Written by: Jessica Hanley | Published:
Both mixed waste and single stream MRFs can now recover nearly 95% of the metals passing through their yards

Collecting, processing and recovering valuable material has spurred a wealth of mixed waste material recovery facilities (MRFs) to install the latest equipment to recover the highest-grade product in municipal solid waste (MSW).

Many MRFs now employ a total metal recovery system to separate, sort and grade fine pieces of metal. Local authorities and councils today utilise some of the most innovative solutions when it comes to the separation of ferrous, non-ferrous, stainless steel, copper wire, aluminium and other valuable metals from the mixed waste stream.

Allocating budget for equipment technology helps local waste recyclers become efficient, low-cost scrap processors – the newer equipment not only saves on energy consumption, but also recovers higher levels of marketable grades of metal and plastics.

Research and development teams from hi-tech manufacturers such as Eriez are responsible for many recycling industry product breakthroughs that decrease the cost of sending unrecovered metals and plastics to landfills, recycle precious materials and produce increased profits for MRFs around the country.

These equipment breakthroughs now maximise recovery, in as small as footprint as possible, while offering efficiency and safety benefits at the same time.

Technology’s payback

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

Technological advancements in separation equipment can now recover valuable ferrous and non-ferrous metals less than 25mm in diameter from the fines waste stream. That means reducing the amount of waste destined for landfill and reclaiming thousands of kilos of metal each day.

Engineers and product technicians from manufacturers of magnetic separator solutions have collaborated with the scientific world to design separation equipment that takes more recyclable material out of the waste stream. In many cases, the metal and plastic fragments are re-sold to product manufacturers and released back into the marketplace.

These manufacturers work closely with OEMs or complete systems providers when recommending metal separation equipment. Technicians consider expected capacities, material compositions, material size and other variables which factor into the type of equipment needed for any MRF.

For example, suspended electromagnets (SEs), drum magnets and eddy current separators are employed in various ways in this particular environment. SE magnets, drum magnets and magnetic pulleys are used when ferrous metals need to be recovered.

An eddy current separator (ECS) is a great choice to separate aluminium cans or other non-ferrous metals. Recent tests conducted at an MRF showed an ECS recovery rate in excess of 99% for used beverage cans.

Recovery methods also include the use of electromagnetic mechanical feeders to help spread and singulate materials to sorters. This equipment is typically installed with other OEM systems at MRFs. The Eriez Metal Loss Monitor, which continually tracks metal losses, counts UBCs or other metals missed by upstream separation equipment.

Separation equipment in tandem

A typical MRF utilises a drum feeder to feed material into the system. These facilities use a series of disc screeners to separate newspaper, cardboard and other waste from the remaining materials.

Use of a Suspended Self-Cleaning Magnet allows for quick and efficient separation and recovery of ferrous material, such as tin-plated steel cans. The magnet is suspended either cross-belt (perpendicular to the product flow) or inline (parallel) above the product flow. These magnets are designed to constantly pick out and remove large chunks of metal from the conveyor belt.

The self-cleaning magnet incorporates a short belt conveyor built around the magnet to effect automatic removal of trapped tramp iron from the magnet face. Magnet strength increases as conveyor belt width and burden depth increase.

Speedy reclamation

Smaller-sized metal is sometimes dropped onto another conveyor, where the material comes into contact with a magnetic head pulley. These pulleys transform a belt conveyor into a powerful self-cleaning magnetic separator.

Ferrous material travelling along the belt conveyor comes within 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.The clean, non-magnetic material is discharged over the pulley in a normal trajectory.

MRFs typically use these magnetic pulleys when high conveyor speeds, heavy burden depths and hard-to-separate ferrous materials are involved.

Also coming into play for high volume ferrous separation are heavy-duty magnetic drum separators. These powerful magnetic drums feature a non-magnetic exterior shell that is driven around a fixed magnetic centre.

Ferrous metals are drawn out of the waste stream by the powerful magnetic centre and held against the revolving shell. The metal is released when it reaches a discharge point beyond the magnetic field.

Permanent deep field magnetic drums are found in many MRF operations. Some models, including those offered by Eriez, contain rare earth permanent magnets and bucking poles to project a deep magnetic field capable of removing ferrous from distances of up to 380mm. The drum shell that contacts the ferrous material is made of heavy manganese steel and is abrasion-resistant for extending operating life.

Eddy current separators

The salvaging process continues when the overflow scrap metal passes through eddy current separators that further separate the non-ferrous materials. In operation, eddy current separators use permanent rare earth magnets that produce repelling forces to provide a cleaner product for further processing.

These units easily separate aluminium from other materials in the process stream. As aluminium cans or other non-ferrous 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 non-ferrous metals are propelled over a splitter for separation.

Eriez’s most recent addition to its line of eddy current separators features an eccentric magnetic rotor for separation of non-ferrous metals at MRFs. The unit is designed with an eccentrically mounted magnetic rotor within the nonconductive larger diameter shell.

This eccentric rotor concentrates its eddy current forces into a zone of separation at the end of the belt. By focusing its field, this design ignores ferrous material in the flow. The eccentric rotor design reduces long-term wear from heated ferrous build-up.

Other eddy current separator models are available for coarse materials greater than 25mm, with a deep field rotor designed for maximum trajectory; and for non-ferrous fines measuring less than 25mm, high-frequency rotor configurations concentrate the eddy currents closer to the belt’s surface, improving separation of this difficult material.

Also part of MRF operations are vibratory feeders, used to feed materials onto magnetic separation equipment as well as onto conveyor belts. OBM feeders and electromagnetic feeders, with their heavy-duty construction, are recommended for multiple applications.

OBM 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. OBM feeders are an ideal choice for spreading materials.

Heavy-duty electromagnetic feeders are an ideal choice to meter plastics regrind. They offer superior feed control and excellent isolation of vibration. These high-quality feeders require minimal maintenance and deliver years of trouble-free performance.

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 landfill.

That’s where some waste recycling operations have installed the Eriez Metal Loss Monitor (MLM) to help confirm those losses. The MLM is typically positioned on the final waste stream in these facilities.

The MLM 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 household waste industry inevitably experiences many challenges with the growing complexity of modern-day product design. However, by investing in the latest separation technology, designed and manufactured for complex separation, it will significantly improve recycling plants’ recovery grade and reduce waste going to landfill.

Jessica Hanley is a marketing executive at Eriez Magnetics Europe.

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