Sorting It Out

The latest innovations and developments in sorting equipment for MRFs

Republic Service’s positive sorting in Plano, TX
Republic Service’s positive sorting in Plano, TX
Van Dyk

The goal of every materials recovery facility is to separate, recover, and prepare the highest quality of recyclable products most efficiently and safely for the lowest cost. Sorting technology, including optical sorters and robotics, is in continuous development to provide higher productivity, but most people in the industry stress that education is needed for optimal results.

“You get better quality seed stock with dual-stream versus single-stream,” says Bob Gardner, senior vice president, SCS Engineers Technology. Sorting at the curb reduces contamination. However, he adds, it requires public education and policing. He says Cleveland has a 90% contamination rate; most recyclables that some residents spend time separating still end up in a landfill due to contamination.

Contamination is widespread. With China’s “National Sword” program placing tighter restrictions on contaminated waste and banning certain kinds of waste from America, some Chinese companies have begun coming here to get a cleaner product, says Felix Hottenstein, sales director for MSS Optical Sorters, the optical sorting division of CP Group. “Poor quality material now goes to a landfill.”

Doing a sort here allows Chinese companies to export only clean, salvageable material. Also, Gardner says, “China purchased paper mills in the US to generate their own pulp.” Owning facilities in America saves space in their home country and adds a level of control over the process. Plus, Gardner points out, “they don’t have to dispose of the residue in China.”

Hottenstein sees this policy as a stimulus to improve the quality of material and the effectiveness of the sorting equipment. “It forces us all to be better.”

Greg Gesell, a mechanical engineer for HDR, agrees—to a point. He believes that recycling economics is driving the issue and that the National Sword is only part of that. “Would the severe price declines have occurred without National Sword? Maybe.”

He suggests re-evaluating our recycling practices to improve quality or return to high quality, as opposed to focusing principally on quantity or landfill diversion. “A lot of inefficient and smaller systems have struggled,” says Gesell, “yet, there still are communities investing in system upgrades or even whole process lines that are investing now in preparation for better times.”

One example Gesell cites as a positive outcome of the National Sword is a facility that was ready to come online with a brand-new mainline sorting system that was expected to maximize diversion and produce large quantities of cardboard and mixed paper, as well as containers of all types. Before they were able to start up, the facility had to acknowledge that the fiber quality from their system was not going to be marketable. They needed to redesign their process and goals. “Expensive, but necessary,” he says, adding that the facility is now able to produce marketable commodities.

China’s increased import standards on recyclables have played a part in creating what Tony Bonds, marketing manager for CP Group, calls “a glut of domestic scrap in the US.” Because domestic demand remains low and the value of mixed paper, plastics, and metals is down, this is a strain on MRF operations. This is why, he adds, “CP Group’s main focus is on designing equipment, MRFs, and material handling processes that maximize recovery for our customers.”

Van Dyk’s non-wrapping screenVan Dyk’s non-wrapping screen

Rising to the Challenge
Years ago, Gesell says it wasn’t possible to achieve Institute of Scrap Recycling Industries Inc. standards for prohibitive materials and outthrows—contaminants—for fiber products. It was also “very difficult” to get specified contamination rates for plastic categories under the operating conditions and with the available equipment for single-stream MRFs—in part because “the focus was mainly on processing quantity and less on quality.”

“Contamination levels of five or eight or even ten percent total outthrows for some materials were not achievable,” says Gesell. “Often, it was agreed to achieve ‘mill acceptance’ when demonstrating performance at a new MRF.” That means that if the mill accepted the commodity, MRF acceptance was achieved. This approach worked as long as the mill didn’t tighten its requirements—but then China did.

Today’s technology is capable of achieving more. When the standard was first imposed, Gesell says few equipment suppliers were willing to step up to the National Sword levels of 0.5% contaminants. It’s different today, although he says it’s important to carefully clarify and define how the required standards will be demonstrated.

Van Dyk’s elliptical separator bounces back 3D material.Van Dyk’s elliptical separator bounces back 3D material.

The ability of a facility to achieve levels of performance that approach the National Sword requirements is often the result of many factors, including more positive sorting where the desired material is sorted from the mixed stream, focus on keeping contamination out of the MRF, lower throughput requirements, and other reasons, as well as better equipment performance capability, Gesell lists. Besides, local education and resident acceptance of quality standards are very important to position a facility so it can achieve high-quality standards.

“Starting with better quality feedstock helps,” notes Gesell, adding that today’s quality requirements demand higher technology facilities for larger MRFs. He believes that careful equipment selection and arrangement will allow for the highest commodity quality guarantees. “Equipment performance should also consider the ability to maintain those performance levels for ongoing operations.”

Van Dyk’s 3-stage Walair systemVan Dyk’s 3-stage Walair system

Screening Process
To improve the quality of materials, there have been “significant changes in optical and robotic sorting,” according to Gardner. Optical sorting of plastics is based on spectral characteristics, he says, and robotics is evolving to minimize labor, health, and safety issues, particularly with items like sharps.

Among the advances SCS has been working on is an application in a Minnesota MRF, where robots segregate bags for household organics, a recycling program, and compost. The optical sorter is programmed for spectral characteristics. “The challenge is weight,” says Gardner, “and speed. How many robots do you need?”

Sensors indicate where items are; robots have to grab them. The issue, Gardner elaborates, is integrating the software to coordinate the mechanical with the optics. “The effectiveness of the optical sorters depends on how deep, wide, and fast the material is on the belt.”

Optical and robotic sorters are only as good as how the material is prepared, states Mark Neitzy, who says that Van Dyk Recycling Solutions is “working on preparation behind the scenes to feed the sorter.”

Van Dyk’s DeftAir assists in material preparation.Van Dyk’s DeftAir assists in material preparation.Van Dyk

A single layer of homogenized material is the easiest to sort. “The material must be single-layer,” emphasizes Neitzy. SCS manufactures equipment that helps make optical sorters and robots more successful through speed, accuracy, and hit rate—including both recovery and purity. Achieving single-layer is one driver, but Neitzy says that “most equipment is bought because of film bags.”

It starts with a sizing screen: 440 mil is the diameter on the rotating shaft needed to eliminate film bags and prepare materials, Neitzy says. “It’s a huge piece of the puzzle.” Next is an elliptical separator, or ballistic separator, with paddles that bounce 3D material back and walk 2D materials up—materials such as film, newspaper, and white paper. He dubs this “intelligent separation” and says that optical sorters “hate floating material.”

After the screen and ballistic separator comes the optical sorter, followed by a “robot quality check,” lists Neitzy. “Robots are good in the right application if the stream is prepared.” To assist with that preparation, the DeftAir—basically a hood on the conveyor belt with fans that run at the same speed as the belts so material stabilizes and more throughput is achieved—allows the optical sorter to go at maximum speed.

Another preparation tool is the WalAir, a density separation device that produces a stream of air, which flows over the drum and goes to the separation box for light, medium, and heavy material. “Companies are ‘lightweighting’ plastic bottles,” points out Neitzy. That results in 5% PET in the wastestream—about 42 bottles per pound, or 1,600 bottles a minute.

“Robots take up space and can only go so fast,” continues Neitzy. In order for them to reach an accuracy percentage in the mid-90s for hit rate and purity, the use of a 9-foot-wide optical sorter with an 800-feet-per-minute belt speed can enable robots to pick up to 2,000 bottles per minute. However, he says 90% of MRFs use only mechanical separation.

CP Group’s answer to sorting is the CP Auger Screen, a one-of-a-kind device that uses a series of flighted, cantilevered augers that don’t wrap, Bonds explains. Designed to fractionate material by size, it is versatile enough to be adapted as a primary screen, scalper, or fines screen.

Also designed to reduce wrapping, the CP Anti-Wrap Screen separates newsprint and large fiber. The large shaft circumference keeps problematic materials from wrapping, which reduces the amount of cleaning and maintenance needed. Replacement of the single bolt-on discs is also quick and simple, Bonds adds.

Separation Anxiety
It has taken years, but Gesell says robotic technology has finally taken off, thanks to better sensors, more successful picking methods, and improved safety. Now, user-friendly robots can be placed next to manual sorters. There are even robots for C&D and e-waste—and they’re becoming more affordable.

However, due to speed limitations and a design that allows them to grab just one item at a time, robots can’t compete with optical sorters in high-volume applications, Gesell believes. “A robot might serve a QC role to complement an optical sorter, grab lower volume materials, or recover missed items on a residue line. In these types of roles, the number of picks per hour may not be as important, but the robot doesn’t get tired and can be trained to look for more than one type of material. The technology does a great job of recognizing many types of commodities [and] can be built to handle all sizes and weights of materials.” Thus, he says, they are being used in innovative applications for all types of recycling operations, not just single-stream applications.

However, it does need to improve the successful picking rate. Nevertheless, Gesell expects ongoing improvements and cost reductions will make it competitive with other sorters and a technology to keep an eye on.

Another sorter that is evolving is the optical sorter, which got its start with high-volume container capture of, specifically, PET water bottles. “They are still the high-volume champion, but now are used in a typical MRF in many high-volume locations for all types of containers and paper in lots of innovative labor-saving applications,” observes Gesell.

What is new about optical sorters is the improvement in sensors, refined housing designs, and arrangements that increase the accuracy and ability to maintain that accuracy, better air distribution, more jets, maintenance needs, and safety. Some early models are being upgraded to improve their performance.

On a sort line, the number of successful picks per minute can be in the thousands—almost what can be properly delivered by the accelerating conveyor, thus replacing multiple sorters. Equipment suppliers are very creative, using teams of optical sorters to capture multiple commodities and subdivide them into specific commodities.

Optical sorts can outperform manual fiber and container sorters in many applications, Gesell says—not only because they can be faster, but also because, if fitted with the right sensors, they can make judgment calls regarding material quality issues.

Sensors are critical for the success of robotic and optical sorters, Gesell firmly believes. “Improving the resolution and speed of sensing has resulted in better near-infrared technology than many of the early offerings were capable of achieving.”

Now NIR is used with color detection in wider spectrums and, when needed, some suppliers can offer other technologies borrowed from food processing, mining, or other industries. A few of the more common technologies include electromagnetic and induction, X-ray (transmission and fluorescence), infrared (heat dissipation or light absorption), specialized lasers, density, hardness, and other techniques to more clearly distinguish the desired materials from contaminants. “Most MRFs don’t need these advanced technologies, but a system designed to allow for future changes is very important,” concludes Gesell.

He provides examples, such as better color sorting and determining if a piece of paper is too wet, dirty, or has too much ink for the particular product. “Or, they can sort types of metal, compost, or e-waste.” PET can be sorted by bottles and by color. Technology can determine if a bottle is half-full; recognize PET labels on other types of containers; identify black PET; distinguish glycol-modified PET-G film, flexible containers, clamshells, sheets, or other types of containers; and determine if the PET object has too much contamination.

These techniques can increase the capture rate, reduce contaminants, broaden the range of products, and further subdivide the products, thereby increasing value for the commodities produced. While many of these techniques may only be fully utilized in very large or specialized sorting, having equipment that is capable of utilizing the techniques is beneficial. For instance, Gesell explains that, while mixed plastics (Nos. 3–7) may not be readily marketed in today’s conditions, polypropylene (PP No. 5) from the mixed plastics general can be sold and separation of polyvinyl chloride (PVC No. 3) and materials containing fire retardants improves the fuel properties of the remaining mixed plastics and MRF residues, potentially reducing the need for landfilling.

Like cell phones, cameras, and TVs, sensors are continuously in development to achieve better resolution, Hottenstein says. Pointing out that MSS Optical Sorters built the first sensor sorter in 1989, he explains how they use infrared lights to identify plastics because different wavelengths reflect differently. “They’re more sophisticated today and scan more quickly with better resolution, tracking smaller particles and more volume.”

The newer machines do things the older ones couldn’t, Hottenstein continues, citing PET bottles with shrink sleeve labels as an example of significant improvement. “It recognizes the bottle behind the label and pulls for recycling. It’s a higher level of sophistication.”

Higher resolution also allows the sorters to see smaller containers and crushed items, as well as pouches with multilayered materials, depending on the design of the package. “The machines perform tasks people can’t—like sorting polyethylene and polypropylene,” says Hottenstein. “They are more effective than manual sorters, with no concerns about repetitiveness or safety.”

In an era when it’s difficult to find manual sorters, this can be a great asset to a MRF. “The machine does most of the work,” says Hottenstein. “People [serve as] quality control.”

Sensors with higher resolution have increased purity levels: 95–98%, Hottenstein claims. But technology costs money, leaving him to pose the question, “Does a higher percentage of purity warrant a new machine?”

Retrofitting MRFs to achieve better quality sorts has become the main source of income for MSS Optical Sorters. A MRF in Indianapolis, IN, that was 10–15 years old and had no sorting equipment was retrofitted with cutting-edge technology. However, Hottenstein says, not every community feels the costs are justified. “If cities decide it’s a challenge—if it costs too much or is too much hassle—they won’t do it.” It’s a value decision, but often, it comes down to money.

For MRF operators interested in boosting the purity of their fiber material, Bonds suggests CIRRUS FiberMax. Designed to deliver a higher level of purity of newspapers and mixed paper, it is up to 40 times faster than manual sorters, with more than 1,000 picks per minute, according to CP Group. It can positively extract mixed paper or sort prohibitives such as plastic bottles, metals, film, and trash.

MSS PlasticMax can also sort almost any type of material, either positively or negatively. The L-VIS and MetalMiner recover metal for ASR, E-scrap, and other industrial applications.

The PrecisionFlow eject hood for optical sorters from MSS controls the trajectory of lightweight materials such as flexible plastic packaging or single sheets of paper. “Because of the optimized shape of the hood, we have much better control of the trajectories inside the PrecisionFlow eject hood. This provides our customers with better separation efficiency, increasing the removal of flexible plastic packaging from contaminated paper streams. It also enhances positive sorting of fiber such as sorted office paper,” says Hottenstein. Independent third-party testing indicates that the eject hood played an important part in the 97% recovery rate of flexible plastic packaging from contaminated paper streams.

Overall, MSS optical sorters have a recovery rate of 94% or higher, but to maximize material recovery, MSS uses high-velocity belt speeds of 1,000 feet per minute to enable improved material distribution and lower belt coverage for minimal loss of good fiber.

Machinex’s optical sorter, the Mach HyspecMachinex’s optical sorter, the Mach HyspecMachinex

Technology: Improvement and Innovation
Film and lightweight sheet paper float. “Film bags don’t get separated from paper; that’s the reason we don’t sell paper to China,” says Neitzy. That’s also why he says optical sorts are being talked about for paper. “You can do a positive sort on paper, using the optical sorter to get paper out of the contamination.” He mentions a newer Plano, TX, MRF that has three lines of positive sorting.

Or, the process can be flipped and the paper can be ejected from the contamination. This method has been successful at two installations. Although he says a positive sort is more effective and gets cleaner paper, he says there is more room for error and it uses more air. Nevertheless, with proper separation and preparation, positive sorting can make paper without film bags.

Unfortunately, he says, most MRFs built from 2002 to 2013 are without the necessary technology to handle bags. With the average system capable of processing 35 tons per hour and an average of 212,000 bags an hour coming to the system, Neitzy estimates that it would require 60 sorters for the film alone.

Machinex’s sorting robot, the SamurAIMachinex’s sorting robot, the SamurAIMachinex

Future Goals
A new MRF in Maine has optical sorters to recover #1 and #2 plastics, ferrous metals such as tin and aluminum, and cardboard for traditional recycling markets. Plastic film is sorted out.

“All else goes to a pulping operation,” indicates Gardner. There, it undergoes additional separation and is sold for fuel. What’s left goes to a landfill. “There are multiple pathways—recycle or pulp. There’s no value in recycling mixed paper; there is only value in the cellulose.” Coastal Resources, the MRF, produces a marketable clean cellulosic pulp product that is reclaimed from mixed paper and sold on the commodities market.

There is additional value in recycling #1 and #2 plastics, metal, and cardboard—if their level of purity is high enough. “Contamination is a big deal,” states Gardner, although he says it’s less of an issue in Maine because of the high volume of mixed paper.

The Maine MRF serves 85 communities, processing approximately 180,000 tons per year with a 70–80% diversion (50% is required). Coastal Resources uses an innovative second-generation recycling technology developed by Fiberight to recover sustainable resources from waste.

Not only does this MRF offer a processing solution for plastic bags and #3–#7 plastics, but organics are also recovered and converted into biofuel. Also, contaminated recyclables without a market are recovered and upgraded into commodities for local markets.

To obtain a usable product, Gardner says it’s imperative to have a system that can separate the different types of materials. Of the four mixed waste processing projects that SCS has installed in two years, each uses a different process.

Whichever process a MRF currently uses, Gardner envisions a “big push” for finer segregation in the future, especially when it involves organics, whether on a commercial or residential scale.

Developing more domestic mills and commodity outlets would help balance the impacts of the foreign markets, Gesell believes. It could also impact purity levels. “Keeping products domestic offers a good answer for the marine plastic issue, as well.”

With recyclables constantly changing, equipment and processes must adapt. As Gesell speculates, time will tell how the current push to avoid all plastics or at least single-use plastics will shape the MRF of the future. One thing is certain: sorting technology will adapt