NOVEMBER/DECEMBER 2007
New and improved detection and separation technologies are creating cleaner and more valuable ferrous and nonferrous commodity streams from shredded scrap.
BY THEODORE FISHER
Not that long ago, anything a magnet couldn’t pick out of shredded scrap was simply considered residue, and it often ended up in a landfill. Then rising nonferrous scrap prices and technological developments like the eddy-current separator made it possible—and profitable—to separate nonferrous metals from shredder fluff. In the past few years, nonferrous prices have surged again, making it even more worthwhile to separate and sell both mixed nonferrous metals and individual streams of aluminum, copper, zinc, stainless steel, and other alloys, spurring further developments in eddy-current and post-eddy-current advanced separators. One new product in development will even pull copper “meatballs” from the ferrous stream. What these technologies have in common, one manufacturer says, is they are “producing higher-grade concentrates, reducing labor, and increasing your metal unit recovery.”
Eddy-Current Evolution
Though the basic design of the eddy-current separator has not changed, manufacturers have improved the technology in recent years with a variety of tweaks and upgrades, starting with the magnets. A new generation of permanent magnetic material made of rare-earth materials such as neodymium-iron-boron remove ferrous materials at higher speeds for faster production rates. “One reason why the eddy current became a phenomenon was because the permanent magnetic material was very, very strong,” one vendor says. “And rare-earth materials turn out to be relatively inexpensive, from China.” Another manufacturer similarly praises the strength and endurance of neodymium magnets, which have replaced the previous generation of barium ferrite and Alnico magnets. “Today we can get higher gauss readings—stronger pull—so we can extract materials that we couldn’t get before,” he says.
One company has installed “wedge design” rotors between the magnets, forcing the magnetic charge both upward and sideways, which it says creates additional strength in less space. “Our narrower eddy can handle capacities that others may need additional width to accomplish,” a company representative says.
A different ECS thinks small: It recovers and separates the fines—ferrous and nonferrous particles as small as 3/8 inch—from fluff particles that might be too small for other detectors. The firm uses “a very special magnet pulley, or rotor assembly, to get some of the weaker magnetics out. Below that is another magnet that gets good steel from [cruddy] magnetic dirt,” a company representative says. The largest users of this system have retrieved up to 3,000 pounds of nonferrous a day from shredder residue. With that kind of result, the system can pay for itself in as little as six months, he says.
Sensor Sorter Advancements
Since about 2000, most shredder yards have been sending their fluff on high-speed conveyors through machines that use metal-detection sensor coils to identify any remaining metals—stainless steel in particular—that the eddy-current separator missed. The sensors typically activate air jets that blow the metal particles away from the fluff. Those first sensor sorter machines usually positioned the air jets above the material stream and blew downward. Newer machines are more likely to position the jets below the stream, “closer to the particle flow to create a cleaner recovered product,” one vendor says. The sensors also are becoming more sensitive, with one manufacturer stating that its system can detect and separate particles as small as 1/8 inch.
Some vendors now offer an alternative to air-jet separation: mechanical contact (airless) separation systems. These products employ motorized paddles, or fingers, which the manufacturers say are ideal for colder climates, where air separator productivity drops in winter. One airless system uses a small motor, a pair of rare-earth magnets, and an electrocoil to power sets of six 2-inch-wide, ultra-high molecular weight polyethylene paddles. “It’s powered up to kind of slap, kick, or push the material,” the vendor says. This system can detect either mixed nonferrous or stainless steel only. The ejection finger sets are easily replaced. Another vendor offers fingers from 2 to 6 inches wide made from stainless steel, aluminum, or composites, with finger size, finger material, and pushing forces matched to the specific application. (Beyond stainless separation, airless systems work with the nonferrous separation technologies described below.)
Cleaner metals, lower labor costs, and fewer headaches are some of the benefits of airless separation, these companies claim. Air systems propel fluff into the recovered metal and blow dust throughout the operating environment, they say. Further, “when you have air sorters, you have to clean the nozzles and do some other things that only higher-tech or higher-grade employees can do,” one vendor says. “With paddles, at the end of the day, the only thing you need to do is take an air hose and just blow everything off—and a regular, low-tech employee can do that.” Airless systems also are less expensive to purchase, install, and operate, he says. A typical 90-inch-wide airless system costs around $250,000—about $50,000 to $100,000 less than air sorters—and can save the customer about $10,000 a year in power, he claims. Vendors of air-jet separation systems counter, however, that air jets can fire “hundreds of times per second,” more rapidly than mechanical fingers can move, allowing the system to capture smaller particles.
Further Nonferrous Separation
Though the mixed nonferrous market is still thriving, at times the market for individual metal commodities can make further separation systems a valuable investment. Two applications of Superman’s favorite skill, X-ray vision, are making this possible.
X-ray transmission systems send energy through the nonferrous stream to analyze each particle’s density, which allows the system to separate aluminum from heavy metals. One XRT manufacturer claims that its machines yield 97 percent pure aluminum, with less than 1 percent ferrous content and less than 1 percent zinc content, according to melt analyses. “It’s a product that’s perfectly suitable for the secondary aluminum market—furnace operators—and the specs are so good they do not need to reshred it,” he says. “They don’t have to liberate any iron because with the XRT you’re able to detect iron content trapped in the middle of the aluminum.” It’s a dry-sorting process that could substitute for the flotation separation a heavy-media plant might perform, he adds.
X-ray fluorescence systems perform spectroscopy analysis by using reflected energy to separate materials based on their chemistry. To clarify the difference between XRT and XRF in metal separation, one vendor explains that “density separations using XRT give you a good indication between light and heavy alloys,” whereas “XRF can literally read and distinguish the major elements of each alloy.” XRF systems can follow XRT machines to further sort the heavy metals into copper, brass, zinc, lead, stainless steel, and ferrous. (Color-sorting technologies now handle that task at some heavy-media plants.)
XRF technology is slower than XRT, one vendor says, but aluminum can be as much as 70 percent of the nonferrous stream, so once it’s extracted by an XRT system, the XRF machine has less work to do. After two years of testing, one vendor expects to install its first scrapyard XRF machines within the year.
X-ray based systems “put processing power in the hands of shredder operators,” one manufacturer says. “Where mixed metals had traditionally gone to a heavy-media plant … we’re now offering a small machine to put at the end of the line that allows increased revenue opportunities for shredder operators” from further nonferrous separation.
Maximizing Benefits
Manufacturers, understandably, make bold claims about the quality of their products. “Our goal is to get 99 percent of the metals in the stream by our processes,” one vendor says. “We actually have exceeded that, with less than 1 percent metal in the waste by weight.”
To obtain that level of performance, yards most likely will need to install several complementary systems and carefully control three criteria: throughput, particle size range, and accuracy. “The three are interdependent,” one supplier says. “For example, a system designed to work well on 3/8- to 1½-inch-size material will suffer in purity of extraction when the input material is allowed to exceed the upper or lower limits.”
Price and Selection
The cost of a downstream processing system comprises three basic elements: capital costs, site costs, and operating costs.
Capital costs, which can range from several hundred thousand to over a million dollars, depend on throughput, split accuracy, extract purity, and piece-size range, among other factors. All this should appear on the vendor’s quotation.
Site costs can vary dramatically according to the size of the system, the layout of the shredder’s yard, and the location of the processor, among other factors. Shredder operators should carefully go over all the details with the system vendor to make sure they know exactly how much it will cost to prepare the site for installation.
Operating costs include consumables (belts, nozzles, paddles, and other replaceable parts), power, compressed air (for the systems that use it), and maintenance.
To make sure you get the downstream separation equipment that meets your needs, base a purchasing decision on these criteria:
Reputation. Years of experience producing metal separators for the scrap industry is a reasonably good indicator of a manufacturer’s reliability—but try to confirm it with word-of-mouth.
Size. Make sure the separator’s capabilities accommodate the particle sizes you are producing.
Numbers. Determine how many sensors, air valves, air nozzles, or paddles the system will need for peak performance.
Service. Does the manufacturer service what it sells? Does it offer remanufactured parts and new replacement parts?
Maintenance. Some units now feature modular parts designed for easy replacement.
Energy requirements. Long-term energy efficiency might justify a larger initial cost.
Further Downstream
What lies ahead for downstream separation? Most likely a combination of new technologies, more innovative applications of existing processes, and even greater labor-saving automation.
Manufacturers expect they will have to respond to shredder operators’ escalating demands. “Customers will look for more ways to guarantee the chemistry of the product,” one manufacturer says. “They’ll look for more ways to recycle nonmetallic fractions coming from automobiles and light iron shredding, to make eco-fuel that can be burned to make energy, to make the quality of the material more assurable, and to eliminate labor safety concerns.”
A few companies are designing XRF systems to remove free and commingled copper (“meatballs”) from shredded ferrous scrap, increasing the value of the ferrous by reducing its copper content, reducing the use of manual pickers, and extracting more high-value copper. One company’s meatball picker system will reportedly have a throughput rate of 150 tons an hour and the capability to separate what can be quite heavy pieces of copper and steel. “Steel mills want less copper” in their ferrous scrap, a vendor explains. “What’s achievable from hand recovery is limited. Technology is becoming important,” and he predicts that mills one day will require it to ensure a higher-quality product.
One manufacturer sees scrapyards using XRT separation equipment to find even more value in shredder fluff, as one of his customers has. “By day they’re taking eddy-current metals and separating the aluminum, and by night they’re processing the shredder fluff stream following the stainless steel separators.” The XRT detects and removes brominated and chlorinated materials from the fluff, he says. “The remainder is appropriate as a high-caloric fuel source for the cement kiln industry” or other waste-to-energy operations, “and it results in about a 70 percent reduction in what would have been landfill material.” Near-infrared technologies are used to perform similar tasks now in Europe, he says. He sees polymer separation and recovery as the next step in minimizing the shredder waste stream. “We’re looking for more recoverable products to increase revenues and reduce landfilling costs,” he says. Both XRT and XRF?vendors say their technologies are suited to that process.
Another manufacturer has seen the future—and it’s totally hands-off. “Our emphasis is to remove labor—hand-picking and the eyes of a worker—from the task of separation,” he says. “While a person’s senses were the best thing the last century had to efficiently, flexibly, and astutely separate metals, this is no longer the case.”
He describes a customer who, by purchasing a separator equipped with a third magnet with a variable rectifier, could eliminate four pickers. “That means they don’t put people in harm’s way and don’t test their resolve and tenacity by making them stand up to work long hours—especially now that companies are running double shifts to take advantage of market conditions.”
In the future, “more and more systems will be completely automatic from one end to another. They’ll run electronically, tell you when to change oil, show everything on cameras, ” he says. “You’ll put raw materials in one end and out the other end will come products.”
Theodore Fischer is a writer based in Silver Spring, Md.
New and improved detection and separation technologies are creating cleaner and more valuable ferrous and nonferrous commodity streams from shredded scrap.