Equipment Focus: Fines Processing

September/October 2015

Newly refined separation technologies have the potential to increase metal recovery from automobile-shredder residue, but recyclers might wonder whether the added value justifies the investment.  

By Kenneth A. Hooker

There was a time when recycling scrap from shredding operations consisted mainly of using magnets to separate and salvage the steel. Downstream processing has evolved through the years, however, allowing recyclers to separate, recover, and sell ever larger portions of the shredder output. With eddy-current systems and sensor-based sorting systems, recyclers have been able to separate nonferrous metals from the stream for about the last 20 years. These methods produce a mixed nonferrous metal product that recyclers can either analyze and sell as is or process further to separate the aluminum, copper, stainless, and zinc. Machines can do that separation quickly and efficiently with X-rays or other sensors to “read” each piece of metal that passes by, identify its composition, and sort it by type. Inductive or sensor-sorter units use bursts of compressed air to direct the sorted metals into separate bins; an alternative approach uses an airless system of electromagnetic paddles instead.

In the United States, processors usually collect the material remaining after such processing and send it to landfills. This automobile-shredder residue, or fluff, is predominantly bits of plastic, foam, glass, dirt, rubber, and so on, but it also contains some ferrous and nonferrous metal. Most of these metal pieces are quite small, and many are attached to nonmetallic material, such as wire insulation.

Until recently, most recyclers considered it either impossible or not cost-effective to recover these metal fines from the ASR. Several companies, mostly European, have developed new machines to retrieve and sort the metallic components from this material—and they say the equipment can more than pay for itself through the quantity and quality of its metal recovery. Now some U.S. shredder operators are investing in this equipment to take advantage of this new potential revenue stream.

Following Europe’s Lead
The United States has been slower to buy into this degree of separation than processors in Europe for a variety of reasons. “It’s partly because the equipment was developed in Europe, but it’s also true that disposal costs are much higher in Europe,” explains one European manufacturer of this separation equipment. “Where landfill disposal costs 50 to 100 euros [about $55 to $110] per ton, saving on disposal costs is usually a primary factor in further processing the fines.” Because disposal of ASR typically is cheaper in the United States, recyclers likely are more motivated by the potential to make money selling more recovered metal than they are by saving money on disposal, he explains.

Also, the European Union’s End-of-Life Vehicles Directive in 2000 set strict requirements for the proportion of vehicles that recyclers must recover by weight, and the law increased those targets over time. As of Jan. 1, 2015, 95 percent of each ELV must be reused or recycled. This created an incentive for European recyclers to both maximize recovery and find more value in the ASR.

Finding more value is something that interests U.S. shredder operators, too. “The recognition of the potential for more revenue from fines metal took a fairly long time in the U.S. but has come about because of tough competition in the shredder business,” this manufacturer says. “Everyone is looking for ways to create some additional margin and perhaps derive some advantage compared to competitors. And in general, this isn’t coming from the shredded scrap, but rather from the ASR. When they’re looking for the potential to retrieve a lot of additional metal, this is typically in the fines.”

It’s worth the effort to recover metal fines from ASR, according to one maker of high-frequency ECS, and the recovered material is far from impossible to sell. In fact, he says, “I think it’s an obligation” for recyclers to try. The recycling business, he explains, relies on three equal parts: sourcing, processing, and selling. “Sourcing the material, you’re on the same level as everybody else,” he says, “and if you want to increase the volume of material you process, you have to pay a little bit more for your scrap than your neighbors and competitors. For … selling, you have to find a market for your materials, but at the end of the day, the buyers and the market set the price. If you want to sell more of your material, you have to accept maybe a little bit lower price.” This makes the processing part—recovering the most metal possible—critical.

One equipment manufacturer says his company has focused on helping recyclers refine shredded materials to reduce their reliance on export markets. “Most auto shredders in the U.S. are just making Zorba or Zurik products and selling them overseas,” he says. “But the U.S. secondary smelters, like aluminum casters and brass and copper smelters, typically need a higher grade of materials.” He notes that machines such as his company’s X-ray sorters automate processes that, in the export market, traditionally were done by hand-sorting on giant sorting tables. “Our equipment for sorting fines [also competes with] ‘heavy media,’ [a] process that requires a lot of space and is very expensive.

Our technology allows companies to use a dry process that’s much less expensive to operate, has a much smaller footprint, and [generates] fewer environmental regulations and concerns about process water that’s used in heavy media,” he says.

Evolving Technologies
For the most part, these machines don’t represent a radical technological shift. Rather, manufacturers are finding ways to refine and improve existing ECS and sensor-sorter technologies to detect and separate smaller metallic fragments.

“The main items we make are high-frequency eddy-current separators, along with some gravity separation equipment,” says a European manufacturer. “Most of the technology used in the recycling industry has been around for years. What’s changed is that now there’s an interest in going after fines, and we’ve been figuring out how to tweak and properly design these technologies [to do so]. Since the very first high-frequency eddys were built, we’ve made a lot of progress. Initially people were looking to process materials maybe ¾ inch and below, then 5/8 inch, ½ inch, ¼ inch, and we can now go even smaller than that, to 1/8 inch. We’re now able to recover metals from bottom ash, which is incinerated domestic waste ash, in which the metals are very fine.”

Another European manufacturer has refined its sensor separator, specifically “the selectivity of our induction coil bar, which is very high and allows us to detect material down to a size of 0.5 mm [1/64 inch]. Our unit is designed specifically to handle small materials, up to 1 inch, and is not designed for bigger materials,” says the company’s managing director.

Another company has developed technology specifically to further liberate copper from insulated wire that remains after ECS and sensor-sorter processing. This company’s director of sales says its equipment also boosts the salable yields of other metals left in ASR. “When material comes off a sensor sorter, it’s not perfectly clean,” he says. By putting the material through a system of mills, the processor can separate recoverable materials with simple density table technology. “We have half a dozen systems set up specifically to recover the insulated copper wire. Depending on the sorting equipment manufacturer and the recycler’s process, that material may have a copper content as low as 25 to 30 percent or as high as 55 percent,” he says. The material can’t be processed in a conventional wire-chopping line, he points out, because it contains stainless steel and other materials that can damage the wire-chopping equipment.

“We also work on recovering the metals that are left in the fine ASR,” which may contain 8 to 10 percent metals, he says. “It consists mostly of 1/8- to 3/16-inch material, but a lot of it is made up of very small brass, copper, aluminum, and stainless steel bits—too small to be picked up through a conventional eddy current or a sensor sorter,” he says. “When we run that kind of material through these mills, it gets balled up into larger particles, which we screen to a size that allows for very accurate separation on a density table. [This process] essentially removes all of the metal, so there’s less than 1 percent metallics left in the waste.”

One major U.S. recycler says his company has put in place new separation technology to maximize the recovery of salable materials. “We use a combination of commercially available equipment and proprietary technology that we’ve developed ourselves,” he says. “I’ve spent the last 15 years looking at what’s left in the byproducts and figuring out technology and processes to recover every single bit of metal in the ASR. We use eddy currents, we use sensor sorters, we use induction sensors and dynamic sensors, and lots of different screening technologies. Pneumatic technologies, ballistic separation techniques, heavy media systems—it’s really an elaborate system that we use to recover every bit of metal in the ASR.”

His company has calculated the benefits of aggressively trying to recover metal fines from ASR. “Separation is really an art, and we’ve developed and refined that art over a period of many years,” he says. “There is still some small amount of metal in what we throw away, but it’s not cost-effective to go after that because it’s de minimis—it’s less than half a percent [of the remaining residue]. We could probably get it down below that by running it through again—and if it was gold, we would—but the value of what’s remaining in our waste wouldn’t cover the costs of electricity, fuel, labor, etc., required to extract it.”

Just this summer, a U.S. manufacturer of separation equipment announced a recovery process for copper wire and fine metals that does not require sensory technology, nor any compressed air. By applying process science and using advanced magnets and eddy-current separators, the company says, the new approach lowers capital and operating expenses so processors that could not afford to recover these metals can now do so.

Preparation and Presentation Are Key
Recovering metallic fines effectively requires some preparatory steps and more careful handling than larger pieces normally require. For one thing, the fines fraction is more likely to be mixed with dirt, plastic, wood, and other light materials, which the processor should remove before sorting the metal, the manufacturers say. Another issue is that ECS and sensor-sorter technologies designed for fines are less tolerant of overloading. For these machines to work properly, pieces of material on the conveyor must be of a similar size and presented in a single layer.

Manufacturers have developed specific equipment to address the first of these issues, the removal of nonmetallics. “One German company we represent makes a de-bulking machine that … removes as much of the inert material as possible before further processing,” says one supplier. “That’s a step that’s really needed, no matter what [other] processing steps are involved, because you’re wanting to recover a metal component of less than 10 percent from material that contains so many different components—foam, plastic, etc. If you can reduce the volume in a simple step up front, it makes the cost of a processing system much less.”

Air aspirators are another tool for this task. They use gravity and air to separate fluff from metallic components. ASR enters the top of the aspirator and falls through a zigzag structure as air currents blow across the material, separating lighter, less-dense components from heavier ones. A cyclone removes the fluff, while the heavier material falls to the bottom and continues downstream for recovery.

Addressing the moisture content of the ASR is another important preparatory step, according to this equipment supplier. “Most shredders in the U.S. use water to keep the dust and fire hazards down. If you have shredder fluff that’s too wet, you’ll get bad results no matter what kind of technology you’re using,” he warns. “We recommend that moisture content be less than 20 percent. Some people put in dryers to dry the fluff, but that has mixed results. Some build a building to store their fluff and let it dry out for a few days before further processing it. I think that’s most effective because it’s a one-time cost, and you’re not having to buy fuel for a direct-fired heater.”

Adding screens that can sort fines to more uniform sizes is also a good idea. If you have two pieces of metal, one 1/16 inch in diameter and the other ¼ inch, “if you look at the two pieces in your hand, they look pretty much the same,” explains an equipment manufacturer. But the former is one-fourth the size of the latter—a 1:4 ratio. For optimal operating conditions, “in the fines fraction, the size ratio should be no more than 1:3—that is, the largest pieces of metal should be no more than three times the size of the smallest ones.”

To avoid overloading the nonferrous recovery system, these sources advise running it separately, offline from the main shredder line, which you can do by placing a dump hopper in front of the conveyor feeding the screener. Although this setup can increase material handling costs, it protects the nonferrous system from shredder surges that can adversely affect its operation.

It also allows you to process material a second time, which can increase the yield. Some facilities, particularly those with larger shredders, run the nonferrous recovery system in line with the shredder but have multiple lines of sorting equipment to better handle the volume of material coming from the shredder.

Making Fines Pay
Opinions vary as to the volume of material a shredding operation must process to justify investing in equipment to recover more fines. One source says the concentration of nonferrous metal in ASR is increasing year by year, making it “mandatory to focus on ASR fines and to separate the metal.” He argues that “even 2,000- to 3,000-hp shredders produce enough material to justify advanced ASR processing.” The key is to design a plant that is flexible and fully automated so as to avoid generating additional labor costs, he says.

For smaller shredders that generate 8 to 10 tons of ASR an hour, the milling process described above could be an economical choice, with a potential payback of less than a year, according to the company’s representative. For plants generating 40 to 60 tons an hour, a sensor sorter makes more sense, he says.

“Usually the quickest return on investment will be setting your plant up to size [the material] correctly and purchasing an eddy current to pull out and separate the fines,” advises a designer of nonferrous recovery systems for shredders. “The additional cost of the equipment completely depends on how the current process is set up.” For example, some shredder operators are able to simply buy an eddy current, a platform, and a few conveyors to process the fines, he says. Others must reconfigure the existing nonferrous system to create the fines to put over the eddy current. “It could be as little as a few hundred thousand dollars. If you need to add screening equipment in order to make that happen, it could be half a million dollars. It’s still a worthwhile investment in nearly every case.”

It’s a good idea to send samples of your ASR to different equipment manufacturers to see what their equipment can do with the material you want to process. “Then we calculate a return on investment based on the tonnages that [the potential customers] run and how much of that material they produce,” the system designer says.

And if you’re not sure whether it’s worth investing in the equipment and effort to further process your fines, the large recycler quoted above suggests an alternative strategy: Outsource the work to a firm like his.

“Unless you’re shredding at least 10,000 tons a month, it’s going to be hard to justify any kind of investment to get beyond Zorba, which you get with an eddy current, and Zurik, which you get from a sensor. Getting down to the wire, which is maybe 1.5 percent to 2 percent of the ASR, you couldn’t justify [it] without at least that volume,” he says. “We buy material from smaller shredding operations and run it through our equipment to recover more of the metal rather than sending it to the landfill. And we price [the ASR purchase] based on what we’re able to recover from it.”

Kenneth A. Hooker is a writer based in Oak Park, Ill.