Chasing Value

Advances in automated metals sorting technology have brought together equipment makers and recyclers in a common effort to keep more metal in the recycling loop.

Several different types of technology are being used at auto shredding plants, electronics recycling facilities and at material recovery facilities (MRFs), where aluminum cans are among the materials in that sometimes very mixed stream.

DOWNSTREAM OF THE AUTO SHREDDER

There are currently between 280 and 300 metal shredding plants in the United States large enough to shred an automobile.

While some of these are idle and many, in the current market, are not running five days per week, the owners of these auto shredding plants have continued to invest in equipment that deploys technology and automation to sort through the shredded metal.

Producers of secondary nonferrous metals, led by the copper and brass industry in China, are hungry for raw material and keeping prices high even in a lackluster global economy.

Shredding plant operators who can upgrade their nonferrous scrap grades will quickly be able to cover the costs of the technology they purchase. They have all done the math, and most have chosen to invest in new technology.

Plant operators can make very different decisions about how to best produce clean steel, copper, brass, aluminum and stainless steel scrap grades from the mixed shredder stream.

Plant operators and their equipment suppliers make decisions based on: which and how many grades of scrap do they wish to produce; how many size fractions they want to split the stream into; how many times do they want the same material to pass through a system; to what extent do they still wish to have people remain involved in hand-picking material; and, of course, how much product purity do they want to achieve.

The answers to these questions help dictate which pieces of equipment are purchased, how many units to buy, and in what order they are arranged to create a system.

Although systems can be configured very differently, there are types of equipment that are commonly used within them. These include:

•    size classification screens;

•    eddy current separators;

•    sensor sorters;

•    X-ray sorters/optical sorters; and

•    density sorters (sink/float; sand).

Size classification screens are not a new technology, but they remain relevant. They come in many forms—such as trommels and vibrating tables or conveyors with drop-through screens. They separate the mixed nonferrous and nonmetallic downstream material into separate size fractions. This allows the separating equipment that will be next in line to do its job better.

Eddy current separators also are by no means “new” technology, but remain vital. Larger shredding plants may have four, six, or even eight eddy current separators on the job. These machines use magnetic force to help nonferrous metal pieces jump off the end of a conveyor belt while the nonmetallic part of the stream drops down in a different direction.

Recycling Today guest author Mark Ridall, who works for United States-based equipment supplier Wendt Corp. (www.wendtcorp.com), helped explain some of the newer sorting technology in an article in the April 2009 edition of Recycling Today.

Ridall noted that sensor-based technology has been used in shredding downstream systems for about 10 years. These devices use electromagnetic sensors to identify nonferrous metals and are particularly adept at isolating stainless steel scrap from the mixed stream. Optical sorting, including the use of X-ray technology, has provided another method of extracting nonferrous metal at shredding plants. X-ray fluorescence (XRF) machines use technology that is also used in hand-held analyzing units. These machines can quickly analyze the surface of a piece of metal and identify the alloy composition, according to Ridall.

X-ray transmission (XRT) units transmit energy through pieces of metal that pass beneath them. The XRT units are calibrated to identify certain metals (by atomic weight). The unit then creates and receives an image of those pieces and shoots them away from the rest of the material with an air nozzle.

Another optical technology that has been used involves charge-coupled devices (CCDs). These optical units detect differences based on color, yielding red, yellow (honey) and white fractions. They are recommended for use on mixed metals that have already passed through the previously-mentioned separation equipment or have passed through a density sorting system, says Ridall.

Density or heavy media systems remain part of the technology used in North America and Europe. Fluids and sands that can separate metals based on their specific gravity attributes can both serve to remove nonmetallic contaminants and separate some nonferrous metals from one another.

ELECTRONIC SCRAP SORTING

Automated sorting technology has also become a key part of systems in which electronic scrap is shredded in North America and Europe.

As with auto shredders, electronic scrap shredding plants are set up in many different ways—operators are often willing to try something new if they believe it can help them capture the most metal and separate it more thoroughly for higher market value.

Much of the technology deployed is similar to what is used at auto shredding plants, with automated sorting equipment that separates by size, magnetic qualities, density or readings produced by optical scanning equipment.

Material is first shredded, perhaps by a low-speed, high-torque shredder or by a wire and cable chopper. The mixed stream that leaves the shredder is then on its way to the downstream system designed by the plant operator in cooperation with key vendors.

United States-based shredding system consultant Peter Prinz operated and helped design auto shredding systems before applying what he learned to electronic scrap shredding plants.

In an article he prepared for Recycling Today for the November 2009 edition, Prinz recommended that, after drum and cross-belt magnets catch the steel content, a method to capture aluminum should be considered next. According to Prinz, “Aluminum makes up from 4 percent to 8 percent of the input material” at an electronics shredding facility.

Prinz recommends having one or two people at sorting stations to remove aluminum capacitors downstream from the magnets but before automated aluminum separation.

Prinz recommends an eddy current separator with a high gauss strength—the higher the better—to catch aluminum before it passes through and becomes essentially a contaminant if it stays mixed with the precious metals.

The stream that remains includes mixed plastics, copper, stainless steel, gold, silver and other metals. Prinz recommends a sophisticated sensor sorter as the right piece of equipment to recover additional metallic material.

After a vibrating conveyor spreads out and disperses the material into an even flow, a sensor sorter (or more than one at larger plants) and a series of air nozzles will separate the remaining metals from the plastic.

Prinz concluded his story with a reminder that while automated equipment is impressive, business owners and managers should never forget the importance of people as they undertake their plans. Wrote Prinz: “The most important part of your system is your shredder crew. When the first piece of equipment arrives, you need to have some of your crew there to help in the set-up and installation. And as more pieces arrive, you add to your crew until you have the whole crew in place, from the person who will be charge to the pickers, helping with the installation. They need to be trained from the ground up and to help not only with the installation of the system but with its start-up and testing. They need to be involved. They need to feel that it is their system. If they feel that way, they will take care of the system and see that it runs smoothly with few or no problems.”

His comments are a reminder that investments in automation offer no guarantee of success. The right people must also be on hand to manage and maintain the process and think critically about how to make it better.

SORTING AT THE MRF

MRFs that handle mixed residential recyclable materials provide yet another example of sorting that is done using size classification, magnetic separation and optical units.

The predominant nonferrous grade heading into MRFs is aluminum used beverage containers (UBCs). Eddy current separators are used to identify and separate UBCs from the other cans and containers in the plant. Single-stream plants have grown in number and size in the United States, and operators of these plants have gained much experience in extracting UBCs from this mixed stream.

However, the UBC recycling rate in the United States remains below 60 percent, with the rest of those aluminum cans being thrown into garbage bins rather than recycling bins.

One effort to capture more UBCs in the United States is being undertaken by Envision Holdings and aluminum company Novelis, both based in the United States. The two companies have partnered on research and development and pilot programs to extract UBCs at landfill sites and waste transfer stations.

Envision’s research found that even in cities where recycling programs try to capture UBCs, there are still many of them heading instead to waste transfer stations and landfills.

The MiniMRF system that Envision has developed is “positioned downstream to recover materials that have already eluded traditional recycling programs and are otherwise destined for landfills,” according to the company. “Currently, the technology targets aluminum cans, steel and a variety of other reusable materials.”

The magnetic technology used is not revolutionary or different from what is used at MRFs. But it has been designed to be easily installed or even portable. The other key is for it to be affordable and to quickly return the investment made by concentrating on aluminum and steel—materials with established markets and sometimes high value.

The MiniMRF is one more new tool in a very large toolbox with an important job to do: To find the nonferrous metal for which metals producers throughout the world are searching.

The author is editor-in-chief of Recycling Today Global Edition and can be contacted at btaylor@gie.net.