Sorting Through the Best Equipment for Recyclables
As increasing diversion goals become harder and harder to attain, there is more and more pressure on efficient separation of recyclables to ensure maximum recovery at a cost that MRF operators can afford.
As increasing diversion goals become harder and harder to attain, there is more and more pressure on efficient separation of recyclables to ensure maximum recovery at a cost that MRF operators can afford.
For municipal sanitation departments, the main Y2K issue may well be the fact that their diversion goals are coming due. And particularly in states where this goal is 50%, that is a matter of some concern. With the market value of recyclables still relatively depressed, materials recovery facility (MRF) operators must squeeze out as much product as possible without significantly adding to their operating costs.
This requires cost-effective equipment and processes to get the maximum quantity of recyclables to the MRF as well as to sort the recyclables and prepare them for market in a form that will generate the highest revenues practical. For too many MRFs around the country, this system primarily consists of conveyors and pickers. Separation is largely a matter of hand-sorting. This situation exists despite the fact that the annual personnel costs of just 10 pickers are roughly equivalent to the annual amortized cost of a million dollars’ worth of capital equipment.
Moreover, there is now a large amount of increasingly capable sorting equipment on the market from which to choose. Some of this equipment represents mature designs that have been developed over the years. The prime example of this unquestionably is magnetics.
Magnetics represent by far the most efficient way of separating tin cans and other ferrous metals from the other recyclables. The two designs that are most widely used are (1) self-cleaning crossbelt permanent magnets and (2) magnetic pulleys. According to Marshall Gralnick of Global Equipment in Boca Raton, FL, a self-cleaning crossbelt magnet located near the start of the line can separate a high percentage of the ferrous metals that may be in the stream while it still contains large amounts of other recyclables. The cost of such a magnet varies with the width of the conveyor belt it is crossing, of course, but Gralnick says a self-cleaning crossbelt magnet for a 48-in. conveyor costs approximately $10,000.
Gralnick also sells magnetic pulleys, but he doesn’t feel they are well suited to a MRF because they have a tendency to trap aluminum cans inside steel cans. However, Diana Spencer of Magnetic Technologies Inc. in Boyne City, MI, believes they have their place. "They offer a practical approach to removing ferrous materials from nonferrous matter being deposited off the end of a conveyor line," she points out. "Thus, although we primarily sell self-cleaning crossbelt magnets to the market, there is a ready market for the lower-cost [starting at $1,000] magnetic pulleys, depending on the application. Although the magnetic pulleys are not guaranteed to get out all the ferrous metal when commingled with a heavy flow of other recyclables at the front end of the line, they can be quite cost-effective at the other end when most of the residual material is itself ferrous.
Ron Harrelson of A&A Magnetics in Woodstock, IL, suggests that the best configuration would be the combination of the two types of magnets. "Use the self-cleaning crossbelt magnetic at the front end of the line right after the paper has been separated out," he explains. "A unit costing between $4,000 and $8,000 should pick up 98 percent of the ferrous then. This helps the gross separation early in the process. Then after the glass and aluminum have been removed, you can effectively use a little $2,000 magnetic pulley at the end of the line to pick up bottle caps and other small ferrous chunks that make up the remaining 2 percent."
Indeed, there is a wide variety of magnetic options available. As shown in the sidebar, "History of Magnetic Materials," there has been a quantum jump in this technology, and there almost seems to be a magnetic product for every separation application.
Eddy-current induction for aluminum sorting is another mature technology that is widely used at MRFs. The cost of an eddy-current separator has steadily decreased over the years, and today’s units will separate virtually 100% of the aluminum in a commingled stream of recyclables. David Chon, president of the consulting firm of David Chon Associates in Baltimore, MD, says he has had clients who achieve payback for this investment in less than a year.
"Eddy-current induction has been around for many years," Gralnick points out. "The principle is quite straightforward. When a conductor is placed in a rotating magnetic field, a current is generated that creates its own magnetic field around that conductor. This induced field reacts with the magnetic field produced by the separator, and the resulting interacting forces have the effect of levitating and ejecting the light, nonferrous metals. As a result, our Master Magnet systems have the extended capability of separating aluminum and other nonferrous metals, such as copper and brass, from each other and from nonmetallic products like plastic, rubber, and glass.
"There are two basic eddy-current designs; one costs about $50,000 and uses a rare-earth ceramic rotor to separate small, shredded nonferrous material. The other, which uses a strontium-ferrite ceramic motor, has less power, but it is ideal for just separating aluminum cans. Since its $25,000 cost requires only half the investment, most MRFs choose this design. They can and do purchase it as a stand-alone unit, but we also offer a complete modular processing system with a fabricated framework containing a vibratory feeder, one of our magnets, and an eddy-current separator. This system removes all the metals, as the ferrous materials are removed prior to the stream reaching the nonferrous separator."
Many MRF operators hand-pick their clear and amber glass from the green glass because it commands higher market prices. Indeed, Chon, who prefers mechanical separation of most recyclables, believes that in the case of glass, hand-separating pays off because the current market for clear and amber is so much higher than for green.
Cynthia Andela of Andela Tool & Machine in Richfield Springs, NY, disagrees, challenging the assumption that manual separation of bottles in a picking line is the only feasible approach. "You have to consider the total costs," she insists. "One person can sort approximately 1,400 pounds per hour of glass. If you’re paying them minimum wage with some benefits, the cost of this manual sorting may be about $10 per ton. Then there are the transportation costs (perhaps $7 per ton) to bring the colored glass to the beneficiator. And there is the cost of transporting the mixed broken glass to the landfill and the tipping costs for disposing of it there. That may well cost as much as $50 per ton."
With curbside pickup of commingled recyclables, a considerable amount of the glass is broken in the truck, and if rotary trommels are used at the MRF, there is still more. In the case of a stream containing 20 tpd of glass, Andela estimates that 40% of the glass that reaches the picking line would be mixed-color broken glass with little market value. Because of all these factors, she calculates that, while the income from the sale of 12 tpd of colored bottles would be $300 per day, the cost of sorting 20 tpd of glass would be more than double that, exceeding the revenues by $344 per day.
The principal differentiator is the transportation and disposal of the mixed broken glass. It represents a dead loss of $440 per day. However, Andela rhetorically asks, "What if the broken glass became a marketable asset rather than a liability? If all the broken glass and the low-value green glass were pulverized, it would be transformed into marketable products that would not have to be landfilled. Therefore, operating costs would be reduced while revenues could be increased."
There is actually a net economic benefit for selectively sorting high-value glass and pulverizing the rest. In the case of the stream with a 20-tpd glass content, Andela calculates that the $344-per-day net cost would be converted into a $142-per-day net gain. How? Although there would be no difference in the financial results of the sorting of the unbroken clear and amber glass, the $462-per-day net loss from disposing of green and broken glass would actually become a small net gain.
However, there is definitely an allure to the higher prices offered for clear and amber glass, and now equipment is becoming available to permit mechanical sorting and separation by color. According to John Willis, vice president of sales and marketing for CP Manufacturing of National City, CA, his company has developed equipment that will "mechanically separate glass from all other recyclables and debris so that an operator can clean up all the glass at his MRF. The equipment air-classifies the unders and then optically color-sorts the clear glass, two colored glasses, and opaques.
"It’s an expensive piece of equipment, though, costing $100,000 to $125,000. A MRF would have to have a volume of at least 10 tpd of glass to achieve payback in a reasonable number of years—unless that MRF is located in California or one of the other states that has bottle laws that pay for redemption. In that case, a MRF with 10 tpd of glass could achieve payback in about 18 months. For MRFs in other states or with a lesser amount of glass to process, we offer two modules of that system. For $40,000, a MRF will be able to buy our sorting module that goes under a trommel and allows sorting out and recapturing of the unders. For $60,000, a MRF can buy the module that detects and rejects ceramics and all other opaque material and thereby sorts the clear glass."
Separation of Plastics
Few MRFs mechanically separate plastics, primarily because their volume of marketable plastics is too low to justify the high-priced mechanical plastic sorters on the market. However, recent events could change this situation. First, tightness in the virgin resin market has sharply increased the value of recycled plastics. High-density polyethylene (HDPE), for example, doubled in price this summer, and some brokers are predicting an even stronger demand this autumn.
Even more significant in California is the state’s enactment of a revamped bottle bill (SB 332) that requires a $0.025-$0.05 deposit on almost all plastic drink containers, including those containing noncarbonated water or fruit juice. Thanks to SB 332 and the trend toward packaging beer in plastic containers, the recovery of plastics in California (and every other state that passes a similar bottle law) should sharply increase. In addition, the development of new plastics technology to eliminate current problems hindering plastics recovery promises to broaden the types of plastic containers and other plastic products and thereby expand the market for recycled plastics.
If so, more MRFs should have the 40 tph of incoming recyclable plastics that Wilfred Poiesz of Van Dyk Baler Corporation of Torrance, CA, estimates is needed to justify the cost of a mechanical separator. "These systems cost 90,000 to 100,000 dollars," he explains. "A light source sends a beam of light that is picked up by a sensor on the other side of the conveyor. That sensor provides feedback to a system that recognizes the material type, directs a blast of air at that object, and blows it over the side of the conveyor into the appropriate bunker. The equipment costs about $100,000 per separation. If a MRF wants to separate five different products, the cost would be 500,000 dollars."
For years, trommels were the only devices widely used to separate paper from the other materials in the stream. But now trommels are not the only option. For example, with General Kinematics Corporation’s patented Finger Screen, the cascading material flows over a series of tapered, slotted finger elements that successfully screen material that would otherwise catch or hang up in a conventional screening device. According to Bill Guptail of General Kinematics, this nonbinding deck is ideal for the separation of commingled waste material and the classification of paper. "Costing only 25,000 dollars for a 5-tph line, the Finger Screen is a less costly alternative to a rotary trommel or disc-type screening device typically used for material classification," he notes. "The primary advantages over a rotary trommel are that it does not break otherwise marketable glass and that it does not ‘fluff’ paper and thereby increase the volume that would have to be handled by subsequent equipment."
Mechanical sorting of fibers from curbside pickup of mixed recyclables requires quite a different process from mechanical separation of containers. In addition to separating the fiber from the containers, it is desirable to have the capability of separating the paper to achieve #6- or #8-grade newsprint as well. Bulk Handling Systems (BHS) of Eugene, OR, has designed such a sorter and now supplies systems built around this newspaper-sorting module. The patented BHS NewSorter separates the newsprint from the mixed containers mechanically, thereby allowing large volumes of mixed recyclables to be processed quickly and efficiently. The NewSorter then performs the labor-saving function of bulk-sorting the mixed material into smaller, more manageable recovery streams containing similar materials.
According to Sean Austin of BHS, the NewSorter contains a series of rotating shaft assemblies containing highly durable urethane discs. The shafts are positioned within a screen chassis and are chain-driven to rotate simultaneously in a forward motion. There is an interface opening between each disc on the same shaft assembly and between reciprocating shaft assemblies that allows small containers, glass shards, bottle caps, and small grit to be removed from the fiber material. The NewSorter operates at an extreme screening angle, causing containers to roll backward off the unit.
Mixed recyclables are fed into the NewSorter by an infeed conveyor, Austin explains. The rotating discs impart a bouncing, wavelike action into the material stream as it is conveyed in a forward motion. This screening action releases even trapped containers through the screening surface and removes the small contaminants from the newsprint. At the same time, the action conveys and discharges the clean newsprint over the top of the screen. The resulting fiber is virtually contaminant-free and will meet or exceed paper-mill requirements.
"However, it achieves 90 to 95 percent sorting efficiencies, thereby improving the quality of fiber to the degree demanded by the paper mills and increasing the safety of the employees hand-picking the sorted paper. With these high separation efficiencies, you increase the productivity of the people and equipment downstream and maintain a high-quality level of the separated recyclables," says Austin.
Single-Stream Processing Systems
The trend that perhaps will have the greatest impact on the separation and processing of recyclables is the move to single-stream collection of recyclables. The theory behind this type of collection is that curbside pickup of mixed recyclables from a single bin will increase productivity and efficiency in collection operations, increase the amount of recyclables that residents will set out, deter scavenging, and reduce the physical demands placed on drivers.
After conducting a pilot study of 4,252 homes to assess the effectiveness of split-stream collection, the City of Los Angeles was so encouraged that it expanded single-stream collection to all 720,000 homes in the city. Now, three years later, the city reports impressive results. According to Customer Relations Manager Daniel Hackney of the Bureau of Sanitation, citywide collection of recyclables has increased by 140% over the two-stream (paper and commingled containers) collection the city had been using. "We will achieve our 50 percent diversion goals by the year’s end," he emphatically asserts.
"And we have saved money in the process," he adds. "By converting our fleet to single-operator automated trucks, we have been able to enlarge our routes from 700 to 1,100 homes, and the trucks no longer go to the MRFs only partially loaded. And we were able to convert the fleet on our normal truck replacement cycle. In fact, the only additional capital costs of the collection program have been the big 90-gallon containers. Operationally, we have realized savings from avoided landfill tipping charges, from flexibility and maintenance economies from our fleet commonality, and from labor savings achieved through attrition as the more efficient operations allow us to eliminate surplus positions. All in all, we have been able to achieve a 25 percent reduction in collection costs despite recycling 140 percent more than we did before."
However, there is a "cost" for these savings in the form of a more complicated and time-consuming process at the MRF. Department of Sanitation Project Manager Antoine Raphael recalls that the MRF contractors’ cost of sorting and processing went up 20% to as much as $75 a ton when they converted to single-stream operations. Part of the cost increase was caused by the new requirement to separate paper from the containers, a time-consuming task when done manually. One of these contractors, Leonard Lang of Sun Valley Paper Stock, recalls that he needed only 25 employees until he started processing single screen. Now he needs 65 temporary workers to augment a permanent staff of 20. Gradually, however, the costs have been coming down as the contractors have trained their crews and begun to invest in mechanical sorting equipment.
Single-Stream System in Los Angeles
The first of these contractors to make such an investment was City Fibers, which operates two facilities under its contract with the city. Designed by the Dutch firm of Bollegraaf and distributed in this country by Van Dyk Baler Corporation, the system is one of the earliest automated single-screen systems in this country. As described by Wilfred Poiesz, Van Dyk’s vice president for the western US, the 25-tph system enables City Fibers to efficiently separate the stream of recyclables into the homogeneous fractions of old corrugated cardboard (OCC), newsprint, other paper, glass, plastic containers, and ferrous and nonferrous metals.
"A belt conveyor feeds the single-stream materials to a primary presorting area where City Fibers’ crews manually remove the large cardboard and waste," Poiesz describes. "The remaining material then goes over our Star Screen system consisting of two beds arranged at steep incline angles. Here, the newspaper is automatically separated from the rest of the stream. The newspaper that has passed over the screens is inspected and manually sorted on a quality control line.
"The mixed paper, finds, and three-dimensional items fall back and through the screen onto a special discharge conveyor. This residue runs over an adjustable oblique or side-angled Star Screen. This unit automatically discharges the glass via a collector conveyor and sends it to a sort line for manual color separation into bunkers. Other materials—largely HDPE, PET, aluminum cans, and ferrous cans—are automatically discharged off the bottom end of the Star Screen and sent to designated sorting areas. Magnets automatically remove the ferrous, an eddy current ejects the aluminum automatically, and plastic containers are manually sorted into colors and types. Fibers, such as high-grade paper and junk mail, travel to the top end of the oblique screen and are manually separated on the mixed-paper sort line. Separated materials in each of the bunkers are then automatically transferred to a Van Dyke baler via a conveyor."
Single-Stream System in San Diego
San Diego has a single-stream system that is being operated by the manufacturer, CP Manufacturing. The system currently processes recyclables collected from 89,000 households, and this single facility will be expanded to handle the recyclables from 290,000 households. "I believe we are the only manufacturer of a single-stream system like this that also operates a system," Willis of CP Manufacturing says. "Operating a system under contract in the real world has given us a unique opportunity to really understand the operational and economic needs of operators and make needed improvements accordingly."
At the front end of the system is a conveyor-fed presort line where pickers manually separate out the OCC. The remaining material is first conveyed to a mechanical newspaper sorter called a NEWScreen to separate out the newspaper to a different conveyor line. The residue then is conveyed to a container/paper screen to separate out the other paper and divert it to another conveyor line. Quality-control sorters at these two conveyor lines pull out any other material that has come through the screens to ensure that the paper products are of readily marketable quality.
The remaining materials (virtually all containers) are then conveyed to CP Manufacturing’s Trom-Mag, which is a combination smooth-bore steel trommel with 2-in. holes and a magnetic separator. Here, small glass shards and dirt are removed, and the steel cans and other ferrous materials are separated. From the Trom-Mag, the remaining material is conveyed into an air classifier system where the lights (aluminum and plastic containers) are separated from the heavies (glass). The lights are blown through an enclosed duct and dropped onto a sort line. Here, the plastic containers are hand-picked and dropped into CP Manufacturing’s perforator-flattener, which causes a 3:1 size reduction that minimizes storage volume and permits faster baling. The remaining material is conveyed to an eddy separator, which mechanically removes the aluminum cans from the residue and passes them to an aluminum flattener.
The glass is sorted by color and dropped into separate bins for trucking to the glass market. For all other sorted materials, a Harris baler is programmed to bale all the different recycled materials. As bins become full, their materials are conveyed to the baler, which can automatically switch from baling one material to another, accommodating the different size, baling, and tying retirements.
"This is a very effective system design that takes full advantage of our key proprietary equipment modules," Willis states. "Consider our Trom-Mag. The magnetic separator is made up of a stainless steel tube welded to the end of the trommel. The Trom-Mag is driven by two chains that wrap around the stainless steel section and by a steel drive sprocket. The chains are approximately 3 feet apart and are connected by 2-inch bar magnets. As the chains drive the Trom-Mag, a magnetic field is created through the stainless steel tube, allowing all the ferrous recyclables to be magnetically attached to the inside of the tube. At the point where the chains and bar magnets leave the tube to go over the drive sprocket, the magnetic field weakens, allowing steel cans and other ferrous metals to drop via a chute into a bin.
"It’s all straightforward and efficient. And like collection with automated sideloaders, it takes most of the labor cost out of the process. We can now achieve rates of a ton per person per hour. We are convinced that the combination of single-bin collection and single-stream separation is the system of the future. It is by far the most cost-effective recycling approach for municipalities as well as private haulers and processors."
Consultant Bruce Mooney isn’t so sure. He believes that the capital costs of an automated single-stream system are too high for most MRF operators. Nor does he believe that rising costs will force automation, pointing out that most MRFs use minimum-wage employees. He believes that capital costs must come down significantly before most municipal MRF operators can afford them. John Hadfield, executive director of the Southeastern Public Service Authority in Chesapeake, VA, agrees. He cites the case of Virginia Beach, which is contracting to process single-stream recyclables, but whose MRF operator is staying with a manual-intensive system. Nor does he believe that municipal budgets will be increased to cover expanded recycling. In fact, he sees interest in recycling waning on the political front. Systems will have to be much more affordable and cost-effective if they are to be widely accepted.
But prices are coming down, contends Poiesz. "Built just a few years ago, MRFs in Phoenix cost $5 million to $9 million and could only process one-third of a ton per person per hour," he recalls. "Now our new plant opening this fall for Potential Industries cost only two million dollars and can process a full ton per person per hour. What’s more, the systems are getting better too. We’ve been improving our system mechanically so that it can stand up to the abrasive environment it faces. And just by eliminating bottlenecks in the flow and implementing automation with small, low-cost computers, we have been able to further increase the throughput.
"And you must remember, not everyone wants the small system with the lowest capital costs. As the tonnage capacity goes up, the operating costs go down. We’re looking forward now to systems of tomorrow that might cost $3 million but will be able to lower operating costs to as low as 25 dollars a ton! For some MRF operators, that will be the most important factor in the separation and recovery of recyclables."
Author's Bio: Author Charles D. Bader is with Dateline II Communications in Los Angeles, CA.