Water gets the squeeze

Auto shredder operators appear to be interested in removing or preventing excess moisture in shredded metals or auto shredder residue (ASR), believing that too much moisture can hinder nonferrous separation.

While adding moisture during shredding is a necessary part of the process, controlling dust and sparks and preventing explosions, recyclers say, it can be too much of a good thing at times.

For example, Dick Reeves of General Kinematics Inc., a Crystal Lake, Illinois-based supplier to the industry, says he’s had several inquiries over the last year from recyclers interested in drying their ASR.

“It becomes easier to convey, to screen and to recover all the metals,” Reeves says of drier ASR. “You’re going for that final whisper of metals that remain in that ASR, and drying it would allow you to recover those materials at a higher percentage.”

Evidence of this trend also exists in a number of separate research and testing programs underway on behalf of shredding equipment companies. As a result of this research, the companies may now offer or will offer solutions to the issue.

Equipment suppliers say their work is based largely on the belief that too much moisture in shredded metals or in ASR makes the material more difficult to sort.

A welcomed side benefit is that drier residual material weighs less, which reduces transportation and disposal costs.

A short list of some companies that have studied the effects of moisture on separating includes Eriez, General Kinematics, Pinnacle Engineering, Sicon and U.S. Shredder and Castings Group.

The amount of moisture within ASR also was highlighted this spring at the Institute of Scrap Recycling Industries (ISRI) 2015 Convention & Exposition, held in April in Vancouver.

Two strategies that have emerged thus far include removing excess moisture from ASR or further regulating the amount of water added during shredding so as to optimize processes while managing costs.
 

Removing the excess

At this year’s ISRI convention, Reeves and Ron Fruit of General Kinematics delivered a presentation on the company’s recent efforts to study the various costs and benefits of removing excess moisture from ASR using a variety of drying methods.

Reeves says the company was inspired to study moisture in ASR after having received several inquiries over the past year about drying ASR using the company’s vibratory and drying equipment.

Reeves says recyclers expressed that moist ASR tends to mat together, trapping wire, making it difficult to separate. ASR also can be difficult to dry uniformly.

“At ISRI we posed the question, ‘is there a benefit to drying ASR,’” he says. “We talked about how we can do this.”

GK conducted tests using customer samples of ASR sent to GK’s facility. The company used fluid bed dryers along with a proprietary system to handle the matted materials. “We were able to apply our technology to allow us to dry that efficiently,” Reeves says of the ASR samples.

The tests involved trying to break up the material while drying the samples to a certain moisture level. The company recorded how long it took for the samples to reach certain moisture levels.

Reeves says GK has developed new technology specifically to handle these difficult materials to achieve a consistently dry ASR.

In addition, the size of the material must be considered, Reeves says, as fines smaller than 10 millimeters respond differently than 2-inch materials. He says the drying systems were generally set up to deal with tighter size ranges produced after screening, as it was difficult to work with widely varying sizes in one drying system.

“You need to have it screened to certain size ranges to be more effective,” he says.

Ultimately, Reeves says, drying the ASR makes it easier to work with while also helping to release trapped metals. He explains that trying to extract metals from ASR with a higher moisture content may cause more contaminants to stick to the recovered metals.

Another benefit of the processes, he says, is that drying ASR also reduces the material’s weight.

Reeves cautions, however, that while technology is available to dry ASR, running a dryer comes at a cost, which increases depending on the tonnage and the amount of moisture being removed.

A related question triggered by the research was how dry the ASR needs to be to facilitate metal recovery, he says, suggesting that producing a bone-dry ASR might not be completely necessary and might even be cost-prohibitive considering the equipment and energy needs. Going from 30 percent moisture to 10 percent moisture is certainly less costly than going from 30 percent down to 1 percent, Reeves says.

GK also studied how long it took to dry ASR to a certain moisture level, such as 10 percent. Knowing the percent of allowable moisture for a specific sample allowed GK engineers to determine the expected residence time and unit size for typical processing volumes, Reeves explains.

“It’s intuitive to think that if we’ve got a dry product, it makes the screening and recovery easier,” Reeves says. “What we don’t know is is there a magic number where we can optimize the system without putting more costs into the dryer.”

However, Reeves says coming up with a target number, whether 10 percent, 15 percent or somewhere in between, might be merited and deserves future study.

“There is definitely an opportunity here,” he says.
 

Regulating moisture

Other shredding and equipment companies also have looked at the issue of moisture at various points in the metals recovery process.

U.S. Shredder and Castings Group, based in Miramar Beach, Florida, also has studied ways to reduce moisture in ASR and the effects that can have on metals recovery, says William Tigner, president of U.S. Shredder.

“We’ve been reducing the need for large amounts of water for years in shredder plants with automated water-injection plants,” Tigner says. “Several projects ago, we decided to measure the recovery rate change of nonferrous metals in a plant before and after the change in water injected in the mill. On this particular shredding plant, when we reduced the water significantly, we noticed a significant change in nonferrous recovery,” Tigner says.

From that point, he adds, the company began looking at deceasing moisture in ASR in more detail.

Tigner says an initial benefit shown in the results of U.S. Shredder’s tests were reduced transportation and tipping fees. Tests indicated an average weight loss of 25 percent, a significant reduction affecting an operator’s removal costs for processed ASR, Tigner says. Improved nonferrous separation also was witnessed.

“When measuring material before and after drying, the dried material allowed preseparation to be much more effective,” Tigner explains, “thus reducing the volume of nonmetallics presented to the eddy currents and sensors, making them more effective.”

While U.S. Shredder’s research in this area continues, Tigner says recyclers making an investment here will need to do their homework, beginning with the volume of ASR to be processed. This figure is directly linked to when the return on investment could be realized, Tigner says.

One company that’s recently launched a product based upon moisture monitoring and control is Eriez of Erie, Pennsylvania. The company’s new Moisture Monitor is part of its SMART (System Monitoring and Reporting Technology) line of products for the recycling industry. According to Eriez, this tool is designed to electronically scan shredded material at a specific point after shredding to measure water content in the stream. When installed on a conveyor, the monitor reports and records the moisture content of the material as a percentage, and this information is relayed to the operator and to internal shredder controls, where it can trigger system changes.

Knowing this moisture level may allow shredders to optimize the amount of water injected into a hammer mill to prevent fires and to control generation of airborne dust while also helping to prevent too much water from being added, which could interfere with separation, increase metal loss and increase ASR weight.

Eriez has been working with controls company Pinnacle Engineering, Cedar Rapids, Iowa, to integrate the findings of its Moisture Monitor with the shredder’s internal watering system, says Scott Tauke, engineering manager with Pinnacle.

Another company that has integrated such strategies in recent years is shredder equipment and integration company Sicon GmbH, based in Germany. The company offers a sensor designed to measure humidity in the bunkers feeding the nonferrous lines, Tauke explains.

Heiner Guschall, managing director of Sicon, confirms that the company has offered its sensor as a part of Sicon’s controls system for more than five years. He explains that it is used to control water injection into the shredder, the operation of the company’s Airsort airsifters and the humidity of the ASR fines ahead of metal fines recovery.

“Just measuring is not sufficient,” Guschall says of the humidity sensor. “The gathered information needs to be part of the automated system to control items like fan speed, temperature of the dryers, etc.”

In Eriez’s case, Tauke says, the Moisture Monitor is typically placed one or two conveyors away from the shredder, within the ferrous line but after the magnets, and on the conveyor headed to the nonferrous separation plant.

John Blicha, director of corporate marketing communications for Eriez, explains, “We try to detect moisture as close to the mill as possible so we can adjust with immediate results to maintain desired moisture content.”

Integrating the findings of the Moisture Monitor with the water-injection control system allows for automatic regulation of the water being added, Tauke says. When used with online systems, he says the control system can prevent the introduction of more water than necessary.

“If there’s too much water in that nonferrous material, everything sticks together,” Tauke says. “As you’re trying to pull the metal out, you’ll have foam and fluff attached to it because of the moisture. The dryer it is, the easier it separates.”

Tauke explains that just about every shredder these days has some sort of intelligent water-injection system. Eriez’s technology is designed so that results from the Moisture Monitor can be integrated into water-injection system controls, triggering them to throttle based on sensor readings.

Tauke also points to the side benefit of reducing the ASR’s water weight.

“Every customer that we’ve talked to has mentioned the landfilling cost reduction as being the big plus,” he observes.

As for a reaching an ideal moisture level, studies continue, but Tauke says it appears that a range of between 10 and 15 percent seems to be ideal from a cost and processing standpoint. What’s more, Tauke says, recyclers’ interest in the capability seems to be high.

In light of today’s lackluster market, he adds, operators are interested in any technology designed to reduce per-ton costs.

“Everyone seems very interested in it,” he says of the Moisture Monitor, indicating that several systems have been installed.

Meanwhile, Blicha explains that having the ability to control moisture in this way gives operators another measure for improving efficiency and controlling costs.

“We believe it’s part of a trend to bring data and analysis into the entire yard, making consistent improvements to the process to maximize efficiency and identify when the systems fall out of preset thresholds so that changes can be made immediately,” Blicha says.

Lisa McKenna, an editor with Recycling Today, can be reached at lmckenna@gie.net.