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Infrared Recycler PUBLIC ACCESS

A Low-Cost Sorter, Designed to Reclaim Tons of Automotive Plastics, Faces a Hurdle Built of PCBs.

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Associate Editor

Mechanical Engineering 122(04), 60-62 (Apr 01, 2000) (3 pages) doi:10.1115/1.2000-APR-5

Salyp N.V., an automotive recycling company in Eiper, Belgium, has developed a mechanical sorting system whose purpose is to recover the mixed thermoplastic portion of automotive shredder residue. Salyp is marketing franchises of its recycling technology to automotive shredders worldwide. The company also envisions an End-of-Life Vehicle (ELV) Foundation, in which auto shredder customers and other interested groups, including government agencies, will help to establish standards for thermoplastics that are reclaimed from auto-shredder residue. Yet the company must overcome a tough hurdle if it’s going to sell its idea to the estimated 200 auto shredders that do business in the United States. A specific section within the law prohibits the manufacture, processing, use or reuse, or distribution in commerce of printed circuit boards (PCB). Salyp plans to combine its thermoplastic sorting system with a system developed by Argonne Lab for the recycling of polyurethane foam. Foam is the third material stream, after metal oxides and thermoplastics, in the initial sorting of shredder waste.

A Belgion company says it has an idea to make more money out of the garbage left by the passing of what the company estimates to be 40 million cars and trucks. Every year that many of the world’s vehicles end their useful lives and make their way to auto dis— mantlers and shredders, who remove reusable parts and materials. The leftovers— some 8.8 million tons of auto shredder residue—are ultimately dropped into landfills.

Salyp N.V., an automotive recycling company in Eiper, Belgium, has developed a mechanical sorting system whose purpose is to recover the mixed thermoplastic portion of automotive shredder residue. The thermoplastics sorting system is a complement to other auto recycling technology that Salyp has licensed from the U.S. Department of Energy’s Argonne National Laboratory in Argonne, Ill.

So far, Salyp is the only licensee of the Argonne technology. The system that Salyp licenses from Argonne separates auto shredder waste into three streams: inorganic fines, mixed thermoplastics, and flexible polyurethane foam. These streams can then undergo further processing for eventual recycling back into useful product. Ultimately, Salyp plans to combine its mechanical thermoplastic sorting system with the Argonne technology.

In the first stage of the sorting system, plastics enter a rotating drum, where they are exposed by an infrared heating element.

Grahic Jump LocationIn the first stage of the sorting system, plastics enter a rotating drum, where they are exposed by an infrared heating element.

Salyp is marketing franchises of its recycling technology to automotive shredders worldwide. The company has put to gether a business plan to establish the ELV (for “End-of-Life Vehicle”) Center, a recycling training and demonstration facility that is scheduled to open at the end of this year in Eiper. The company also envisions an ELV Foundation, in which auto shredder customers and other interested groups, including government agencies, will help to establish standards for thermoplastics (as well as thermosets, foam, and metals) that are reclaimed from auto shredder residue.

Salyp’s thermoplastic sorter was developed in partnership with Oekutec GmbH of Seigen, Germany.

The system can separate large quantities of mixed thermoplastics to 99 percent purity, Salyp said. A key advantage of the system is that it uses a relatively simple approach that eliminates costs traditionally associated with recycling post-consumer plastics, according to Ivan Van- herpe, project manager of the Salyp ELV Center.

Yet the company has to overcome a tough hurdle if it’s going to sell its idea to the estimated 200 auto shredders that do business in the United States. The somewhat knotty issue is contamination by polychlorinated biphenyls, which may be present in shredder waste streams. PCBs are covered by the U.S. Toxic Substances Control Act, a law on the books since the 1970s that deals with many toxic substances on a general basis. A specific section within the law prohibits the manufacture, processing, use or reuse, or distribution in commerce of PCBs.

According to Sara L. McGurk, a chemist at the U.S. Environmental Protection Agency in Washington, who has advised Argonne National Laboratory on the issue, incoming waste must contain less than 2 parts per million PCB for the shredded material to be processed and distributed in commerce as a new product without EPA approval. The 2 ppm level is recognized by the EPA as the lowest concentration at which PCBs can reliably and inexpensively be quantified in most materials and media.

The 2 ppm concentration applies to the waste stream before it reaches the shredder, McGurk emphasized. “Once it gets shredded, you may have a problem with dilution,” she said. “EPA doesn’t allow the dilution of PCBs” —in other words, mixing it with other materials that would reduce the original concentration level of the PCBs. By the time material harboring PCBs has been recycled, the concentration may have been diluted from what was in the original incoming waste stream. In the meantime, PCBs may have been processed and distributed in commerce, both of which are illegal activities, McGurk said. She added that the law could apply to all the products recovered from the auto shredder residue: plastics, polyurethane foam, and iron oxides, if the original incoming waste stream contained PCBs at detectable levels.

EPA regulations generally restrict the options for disposal of PCBs. Shredder fluff that contains PCBs must be burned, or dumped in a special landfill, unless a company applies to the EPA for approval of an alternative method.

Vanherpe said that the ELV Center will comply with the environmental standard, both in the United States and in Europe, where rules regulating PCBs are not as stringent. “We don’t want to risk contamination by PCBs in shredder residue or in future plastics products,” he said. In his view, this can be achieved by removing hazardous materials and incorporating a sensor technology to detect the presence of PCBs in the waste stream.

The thermoplastics sorting system uses infrared energy to heat and dry a washed stream of mixed thermoplastics. The mixed stream is irradiated to a point in which a single type of plastic in the mix—say, polypropylene—is softened, but not melted. Following the heating stage, the mixed plastic stream is fed through a set of rollers. The targeted, softened plastic sticks to the roller and is removed from the stream. The remaining mix continues through the process, which progressively heats and separates the next desired plastic, until all the components in the mix are separated from each other.

Softened thermoplastic attaches to a ste el roller. It is scraped off the roller, flattened into a sheet, and then stamped into pellets.

Grahic Jump LocationSoftened thermoplastic attaches to a ste el roller. It is scraped off the roller, flattened into a sheet, and then stamped into pellets.

Infrared heat, which is well established in other areas of industry, such as automotive paint drying, offers several advantages for heating, drying, and separating thermoplastics, according to Urban Strieker, owner of Oekutec. Many thermoplastics have similar densities, making them difficult to separate with density-based sorting techniques, but each variety of plastic has its own unique peak of IR absorption, Strieker said. IR energy can heat the plastics selectively.

Standard infrared radiators—which can be ceramic, glass, or metal—emit different IR wavelengths. Overall, IR wavelengths range between 0.8 and 7 microns, according to Strieker. Based on the distinction of peak wavelength, short wavelengths range from 0.8 to 2 pm; medium wavelengths cover 2 to 4 pm; and long wavelengths are greater than 4 pm. The short, medium, and long wavelength IR emissions can be used to soften specific types of thermoplastics. For example, glass emitters at 1.2 pm effectively heat polypropylene; polystyrene can be heated by ceramic emitters at 3.2 pm. “Using the right infrared emission frequency, we can match the material absorption lines to provide selective heating to one type of plastics only,” Strieker explained.

Another advantage of infrared energy is that it is highly efficient, Strieker added. It can dry plastics in a matter of minutes compared with hours for conventional hot air convection techniques.

The first stage of the sorting system is an infrared rotary dryer, a rotating drum that contains an infrared heating element, which is designed to heat large quantities of free-flowing plastics. The plastics would be separated from the mass of automotive shredder residue in the system developed by Argonne. In that system, plastic pieces are separated from the auto shredder residue as it passes through a trommel. The plastic pieces fall through slots in the trommel and are conveyed to a magnetic pulley, which removes ferrous pieces that might have remained mixed with the plastics. Mixed plastic pieces entering the Oekutec-Salyp thermoplastic sorting system are about 12 mm in diameter, Strieker said.

The mixed plastic is fed into one end of the dryer. A screw action moves the stream through the rotating drum and churns the material for maximum exposure to the IR heat source. The plastic never comes into direct contact with the heating element. The heated and dried mixed plastic exits the drum at the far end.

“We have a constant mixing stream inside the rotary drum,” explained Strieker. “And we have infrared light close to the constantly moving particles.” He said that infrared energy penetrates about 5 mm into the plastic, providing good absorption of the IR energy.

The heated plastic exits the tube onto a flat conveyor, which passes between two rollers. The top roller is heated and has a textured steel surface. The belt has a flexible under-mat to accommodate the plastic mix traveling between the rollers. As the plastic mix passes under the roller, a combination of heat and pressure between the rolls causes the softened plastic to attach to the upper roller’s patterned surface, separating out the desired softened plastic.

Strieker called this “mechanical fixing.” The softened plastic is heated, but not to its melting point, so it becomes elastic but not tacky.

The separated plastic is then mechanically scraped off the roller, onto a second conveyor. Here the separated plastics, which already contain energy from the drum, are exposed to more IR heat, and are flattened into a sheet by another set of rollers. The plastic is not brought to its melting point. The sheet of homogeneous plastics is then stamped into pellets of about 0.5 in. diameter.

Meanwhile, the remaining stream of plastics will continue down the original conveyor, where the process can be repeated. Although Salyp has so far demonstrated a one-stage system separating just two thermoplastics from each other, Strieker envisions a system that can be expanded to recover any number of thermoplastics. Essentially, the main conveyor belt can be extended, with extra rollers located along the belt and additional IR emitters placed above it. As the plastic mix moves down the conveyor, it will be exposed to progressively higher temperatures and specific wavelengths to soften the targeted plastic. At each roller, a secondary conveyor would be located to move the plastic to the stamping station.

For example, to separate three plastics—polypropylene, polycarbonate, and thermosets—the mix will be heated to about 125 to 130°C, to soften the polypropylene. After the polypropylene is removed from the mix, it is collected, pressed together into a sheet, and stamped into pellets. The remaining mix of polycarbonate and thermosets would be heated to between 160 and 170°C, at which point the polycarbonate softens. The softened polycarbonate passes under a roller, is separated from the thermoset, formed into a sheet, and stamped. The remainder is thermoset, which cannot be softened, and would constitute the last stream. Although thermoset cannot be melted and reformed, it has some recycling value. It can be ground up and used as inert filler, for example.

This approach offers several advantages for plastics recycling. Thermoplastics lose some of their desirable properties when they are remelted. Polymer degradation that results from shearing is avoided because thermoplastics sorted by Salyp’s method only soften, and do not melt, according to Strieker. The avoidance of melting results in higher- quality recycled product, he said. He sees this as a key difference between his company’s approach and a separation technology based on melting the plastic and extruding it.

The components in a mixed plastic stream can vary, depending on the source of material. The modules in Salyp’s sorting system can be switched on or off depending on the availability of raw material.

One potential barrier to returning the plastic to the market are PCBs in the automotive shredder residue, acknowledged Vanherpe of Salyp. The system would have to include quality controls and other devices so that shredders can monitor their recycle streams for PCBs, he said. Salyp so far has not completed that technology.

A prototype plastic sorting system has been demonstrated in Stuttgart, Germany. A larger system is being built to sort plastic from bumpers.

Grahic Jump LocationA prototype plastic sorting system has been demonstrated in Stuttgart, Germany. A larger system is being built to sort plastic from bumpers.

Salyp claims its sorting technology can recycle plastics at one-third the cost of conventional recycling systems. Normal collection expenses are eliminated because the system can be located in auto shredder yards, near the residue source. Costly manual separation and more elaborate identification techniques based on spectroscopic analysis can be replaced by the low-tech mechanical sorting system, according to the company. Its goal is to provide high-quality recycled plastic at half the cost of virgin resin.

The company introduced its recycling system last September at a recycling trade show in Stuttgart, Germany, where it demonstrated separating polypropylene from polycarbonate. Late this year or early next, Salyp plans to build a 1,000 pound-per-hour system to sort auto bumpers, which it expects to be its first application. It will follow this with a 3,000 pound-per-hour plastics sorting system in 2002.

Salyp plans to combine its thermoplastic sorting system with a system developed by Argonne Lab for the recycling of polyurethane foam. Foam is the third material stream, after metal oxides and thermoplastics, in the initial sorting of shredder waste.

After the foam leaves the trommel, it enters the next stage for cleaning. As much as half the weight of the foam in the waste stream consists of dirt, automotive fluids, and moisture. The foam passes over a magnetic pulley, which pulls out leftover ferrous materials. It is then sent to a shredder, where it is reduced to a size of 2 to 5 inches. It then is conveyed to a washing station, where the foam is cleaned of solid particles and oil is skimmed. After washing, the foam is rinsed, dried, and baled.

All that sounds promising. In the United States, however, the key issue will be working with waste streams that are free of PCBs to begin with.

Copyright © 2000 by ASME
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