Charged for separation

Features - Sorting Equipment Focus

Electrostatic separators offer the potential for more profit from used cable scrap.

As the science of cable recycling has advanced and the volume of cable scrap recycled has increased, new processing technology to yield increased recovery can pay dividends. Therefore, it is not surprising that recyclers of this material increasingly are attempting to recover virtually 100 percent of the valuable copper, including what is left behind in the plastic insulation.

It is possible to recover residual copper from insulation in a dry process using electrostatic separators, such as the Hamos KWS electrostatic separator.
 

Copper recycling process

Prior to the use of electrostatic separation, cables must be ground until the copper falls away from the insulation. Thin wires in particular require fine granulation to loosen the mechanical bond between the copper wire and the plastic insulation.

After granulation, copper and plastic are separated by gravity using setting tables. The setting tables are adjusted to produce copper that is as much as 100 percent pure. This is especially important because even the smallest impurities in the copper fraction lead to significant revenue reduction. Copper smelters pay the highest prices for No. 1 copper, so the aim is to produce copper of maximum purity.

For technical reasons, however, it is difficult to produce copper with 100 percent purity while also producing a “copper-free” plastic fraction using a gravity separation table. Particularly when processing mixed cables (namely cables containing course and fine wires and strands) or thin telephone cables, a recycler can expect to lose a small amount of fine copper wire and dust to the insulation. Typical copper losses can—depending on cable type—range from 2 percent to 12 percent, a proportion that implies significant financial losses as processing volumes increase.

Dry electrostatic separators can provide economical separation of even the smallest and finest residual copper particles from cable scrap.

Wet separation methods, such as so-called “water tables,” require further processing of wet plastics, which may not be economical in light of the additional drying time required. In addition, problems can arise with this method if ambient temperatures are low.

Dry electrostatic metal separators use conductivity differences between metal and plastic to achieve separation. After electrostatically charging the fractions with high voltage, the metal and plastic fractions subsequently discharge on a fixed roll surface. While metal particles discharge immediately and fall off the roll surface, the plastic particles discharge slowly and adhere to the roll surface.

Purity of the individual separated products is adjusted to an optimal level using splitters. The separated plastic fractions are extracted from the equipment with integrated conveying screws, causing the metal fraction to fall to the bottom of a container located underneath the equipment.

Electrostatic separators are available in different sizes and with throughput levels. Typical production machines separate at a rate of 1,760 to 2,200 pounds per hour. Throughput rates of several tons per hour can be achieved by using high-performance equipment and installing several separators parallel to one another.
 

Building a showcase

MTB Recycling, based in Trept, France, manufactures granulation equipment and recycles wire and cable scrap. With an annual recycling capacity of 40,000 metric tons, MTB is one of the largest European cable recycling companies.

Jean-Philippe Fusier, CEO of MTB, recently installed several Hamos KWS electrostatic separators.

MTB Recycling adds dual-stage cable line

MTB Recycling, one of the largest cable recyclers in Europe, installed a new copper cable recycling line at the company’s headquarters in Trept, France, in 2014. Designed to handle 25,000 metric tons of cables per year, it also is built as a showpiece for potential customers, the company says.

The line begins with a high-capacity MTB BDR2400R preshredder—an upgrade from the company’s BDR2400U shredder—which prepares material for the next granulation step, according to MTB. This newer model offers a greater rotor diameter, higher cutting blades, a heavier flywheel and more powerful electrical motor to achieve extremely high throughput.

Next, an SRP2400 granulator carries out a sharper size reduction at high capacities. The SRP line includes many features from BDR-series shredders, though it includes the addition of a second stator, an increased cutting diameter and higher cutting speed, the company says. The granulator also features a hydraulic pusher adapted to crushing precut products that helps prevent material buildup. The two machines yield 15-millimeter cable particles up to a rate of 25 metric tons per hour, MTB says.

After sorting the metals from the plastics using air density separation, two electrostatic separation steps are completed. The first step uses three KWS electrostatic separators to retrieve remaining metals from the plastic stream. By adding screens onto the output flows, MTB says it can recover nearly all metals out of what is present in the plastics (around 2 percent). Then, two EKS electrostatic plastic separators sort the plastic stream into two output types.

“After installation of the Hamos electrostatic separators at the end of our copper cable line, we separate all the fine and extremely fine metal particles, even metal dust, from cable insulation,” Fusier says.

“In the past we have lost all this copper together with the residual insulation material,” he continues.

“Our Hamos KWS electrostatic separators recover the valuable metal fractions in the simplest way and simultaneously produce a metal-free plastic product.”

Fusier says MTB was able to earn a return on its investment in a matter of several months.

Because postconsumer cable plastics are a complex mixture of polyvinyl chloride (PVC), rubber, polyethylene (PE), cross-linked PE and many other plastics, the material is recycled in low-grade applications, such as traffic sign pedestals, or disposed of.

In recent months, MTB has been working to find end markets for the PVC insulation it recovers from the cables it processes.

To produce purer recovered PVC products, MTB has invested in Hamos EKS electrostatic plastic separators, which are designed to enrich or upgrade the PVC content from mixed cable regrind materials.

“We have high amounts of cable scrap coming directly from cable production,” Fusier says. “We process such cleaner input materials separate from postconsumer cables.”

He adds that old cables may have a chemical composition that is not compatible with today’s modern PVC materials.

Fusier continues, “After metal separation the residual insulation is now separated in a clean PVC fraction, using our new electrostatic plastic separators.”

He says the EKS process is based on the PVC fraction becoming predominantly negatively charged in a specially developed charging unit. Meanwhile, rubber, PE and other foreign plastics in the mixed material take on positive charges. Subsequent separation in a high-voltage field results in highly enriched PVC fractions and PVC-depleted residual plastics. The concentrated PVC is now extruded to pellets, while residual nonmelting impurities are separated by melt filtration, Fusier explains. (This activity is completed with an industrial partner, Fusier points out.)

He adds that because of good surface quality and superior technical properties, the extruded material from the PVC pellets reaches a quality level that is close to virgin material.

“I am sure that there are numerous new application possibilities beyond the present use of traffic sign pedestals and similar applications,” he says. “We are in close contact with several potential end users, producing more complex and filigree-structure products made of these PVC concentrates. I hope to build up a new customer base for this clean cable PVC.”

In the United States, Hamos KWS electrostatic separators are sold by Copper Recovery Inc., Huntington Beach, California.

Chris Carlson, CEO and managing director of Copper Recovery, also operates his own cable recycling line and has been using KWS electrostatic systems for metal recovery for several years.

“We use our electrostatic separator all the time in production,” Carlson says. “We have calculated the separation cost per hour to be well below $25.”

He says this price encompasses all costs, including financing and depreciation.

“Due to these low operating costs combined with high metal recovery rates, our electrostatic separator has amortized after just a few weeks of operation,” Carlson adds.

He says Copper Recovery has a small scale KWS system available for use by customers who are interested in running small samples of their material.

The copper yield from cable recycling plants, therefore, can be increased with the aid of electrostatic separation technology. Because of its dry operation, recovery of nearly all residual metals, high operational efficiency and, in particular, the rapid amortization of such electrostatic separators for metal separation, the technology can serve as a complement to modern cable scrap processing plants.

Should the cable’s plastic insulation not be disposed of but made into a product, electrostatic separation technology can be applied in this area as well.


 

The author is managing director of Hamos GmbH, based in Penzberg, Germany, and can be reached at dr.k@hamos.com. A version of this article first appeared in the March/April 2015 issue of Recycling Today Global Edition, a sister publication to Recycling Today.