Sorting Systems for Single-Stream Recyclables by Mark Henricks

Single-stream collection of materials promises to greatly increase participation rates for municipal recycling programs. Consumers have been shown to nearly double the amount of material they divert away from landfills and into recycling in communities where single-stream recycling programs have been initiated.

But commingling paper, glass, plastic, metals and other recyclables in a single curbside container also poses problems. While participation rates usually rise, so does the amount of waste generated by the recycling effort. Plus, the recycled material may not be as pure, which creates headaches for the glassmakers, paper plants and others who would reuse the materials.

One solution to the single-stream conundrum is effective sorting of recyclable materials. At National Recovery Technologies, Inc. (NRT) in Nashville, Tennessee, engineering manager John Thomsen says their Multi Sort IR and Multi Sort IR ES Combo and Spyder machines are the most likely to go into single-stream applications. “The main issue we confront is that containers, plastic bottles and other similar sized objects end up in a stream that needs to be sorted by polymer and other characteristics, says Thomsen.” “The part of that that we do is to take out various polymers.”

Sorting PET is usually done first with the Multi Sort IR using transmitted infrared. “We consider that a more reliable detection method. However, its use is limited to the transparent and translucent objects,” notes Thomsen. In a multi-stage process, materials are then immediately separated into transparent and opaque objects. The Spyder can be used for further separation. “Instead of separating the objects by color or transparency, it is looking at the actual polymers,” says Thomsen. For each detection system, controlled compressed air jets are used to physically separate materials from the rest of the stream.

NRT has long sold sorting equipment to companies reclaiming mixed bales of recycling materials, and now is seeing good growth from municipal and other mixed recycling facilities. “Lately we’ve been very busy,” Thomsen says. “This has always been a cyclical business driven by the value of the commodities being processed and public interest and policy in recycling. Both of those are currently driving an increase in this kind of business.”

At General Kinematics in Crystal Lake, Illinois, market director Bill Guptail says the company’s vibratory finger screeners and destoner classifiers are the main General Kinematics products sold for single-stream sorting applications. Finger screeners size items for better downstream recovery, while destoner classifiers are used to separate glass and other heavy items.

“In a smaller facility where they’re going to run different items such as commercial waste, we’ll get a high percentage of old cardboard cartons (OCC) to go over the top of the screen and a high percentage of newspapers to go through,” he says. “If it’s traditional single-stream, where there’s no OCC, we’ll do a different size and get newspaper to go over the top of the screen and rigid commingled materials to go through.”

Typically, materials are sent to optical sorters for further separation after General Kinematics’ vibratory screeners do some of the heavy lifting. “That improves the ability of the downstream equipment,” Guptail says of multi-step sorting that starts with General Kinematics equipment.

Glass is a special problem in single-stream, and one addressed by Andela Products Ltd. in Richfield Springs, New York. Andela’s GP1 & GP2 glass pulverizers plus trammels reduce glass in mixed streams of recycling materials to 3/8th inch or less fragments and also removes sharp edges. Then the glass is easier to separate using simple screens. After dropping out of the stream, the mixed glass is turned into useful products such as roadbed, cover, mulch, pipe bedding as well as sandblasting & water filtration media.

Cynthia Andela, president and chief operating officer, says, “In single-stream recycling, the glass is a lot of times forgotten. It’s hard to get it out of the stream because it’s all broken and mixed in with paper and other things. We can put our equipment in to drive the glass to smaller sizes, all the way down to 3/8th inch size and it doesn’t have any sharp edges. Then we can screen it out. You have simple mechanical separation.”

Andela’s system capacities vary from 1 ton per hour to 20 tons per hour. All comprise three major steps. First, there is a hopper where material enters and is metered. Next, a pulverizer breaks down glass and rounds edges. Finally, there is a screening unit where glass falls through holes and out of the material stream. Conveyors tie it all together. Andela’s pulverizer breaks the glass only while leaving most other materials such as paper and plastic alone. “We put a magnet in the front of our systems to pull out the major steel. Soft cans and things like that aren’t a problem,” Andela says.

Andela’s business has changed mostly in the way recycling materials are being handled. “There’s been a shift over the last four or five years to single-stream recycling because you have a higher recycling rate at the curb,” she says. “But it also means the material is more mixed and the systems to separate it become more expensive and more involved. It’s brought to the forefront the necessity of providing for value-added products.” With that in mind, she spends much of her time developing and educating recyclers about viable applications for mixed glass recovered from single-stream recycling systems.

At Karl W. Schmidt & Associates Inc. in Commerce City, Colorado, national sales manager Jeffrey Van Galder says the company integrates sorting equipment from several European manufacturers into the conveyor belt systems it makes for single-stream applications. Schmidt offers sorters based on technologies including magnetic, eddy current, disk screens, ballistic separators and optical.

Ballistic separators appeal to customers struggling with disk separators that experienced frequent downtime due to wire, plastic ties and plastic bags wrapping around the disks and axles. “Ballistic separation applies high frequency agitation to the material through the use of paddles rather than disks,” he explains. “We wanted to have an option for people that were frustrated with disk screens.”

One of Schmidt’s most active markets consists of smaller single-stream sorting centers processing up to 200 tons a day, Van Galder says. He looks for growth to continue. “There’s going to be an ongoing high demand for these materials and it comes back to collection and making it easy for the material to enter the recycling stream,” he says. “I think single-stream is going to keep on rolling.”