How sorting technologies are changing C&D recycling

C&D recycling systems have evolved slowly but steadily over the years. When you consider the materials generated from demoed buildings, renovations and new construction, it is easy to appreciate what it takes for a sorting system to separate out constituent materials of value while minimizing the associated residual wastes destined for the landfill.

A recent history of innovation

The challenge has always been how to get C&D recycling equipment to do more, so people could do less. Adding a low-speed shredder at the front end of the system was a big step in the right direction for many in the industry, as it helped regulate the size and flow of a waste stream that is by nature, a hodgepodge of contrasts—big vs. small, heavy vs. light and valuable vs. costly to dispose.

Those running systems without shredders commonly added steel Z-pan apron feeders to help provide a metered, more uniform flow to downstream equipment and workers. These systems’ low feed heights enabled excavator operators to better see and control the material mix and flow going to the screen(s).

Over time, the single line systems morphed into dual line C&D systems. Here, the “B line” was added to mechanically capture the small- and medium-size metals and aggregates that would have previously been easily missed by human hands. This addition helped impact the dual line system’s overall recovery rates and increased profitability.

The conventional wisdom has always been “the more magnets the better.” Similarly, density separators on B lines have become equally as ubiquitous, as they mechanically recover aggregates ranging from the size of a finger to the size of a head, efficiently separating by density in the process. As landfill tip rates are typically based on weight, keeping heavy aggregates out of the residuals directly impacts recyclers’ bottom lines.

Ever in search of ways to further increase the recovery of metals and aggregates, a few additional trends have taken root. C&D recyclers have toe-dipped into adding eddy current separators on their B line lights to mechanically capture the nonferrous metals which could otherwise be easily missed. The same goes for optical sorters, which are mostly utilized for capturing hand-size and smaller grade-A wood.

Additionally, many recyclers have added rubber mat secondary (or in some cases, tertiary) screens, with two goals in mind: One, smaller fines remove the “blowables” which can be objectionable to landfills. Secondly, more acute fine screening gives small aggregates a chance to become a revenue-generating product rather than an added expense to the disposal bill. In many systems, these aggregates are captured by the density separator already in the system.

The arrival of new solutions

Until recently, each of these technology advancements in C&D have been squarely aimed at improving recovery rates of the small- to medium-size stream. After all, how could a piece of machinery possibly be tasked with dealing with the infinitely variable stream consisting of large material on the A line?

If you’ve watched a C&D sorting system in operation over the past 20 years, you’ve no doubt been struck by the difficulty of the job the sorters on the manual A line have. In a 5-second window, it might not be unusual to see slowly passing concrete slabs, cardboard, tarp, carpet, pallets, two-by-fours, paint cans, toys, bikes, scrap metals, chimney pieces, film plastic, toilets and more rolling down the line.

Conventional wisdom had until recently dictated that only humans could possibly deal with the nature of the material mix and burden depth of the manual sort line. But as robots began being added to recycling systems of other waste streams, some innovative equipment manufacturers in the C&D recycling space began exploring how robots might help solve this problem for C&D recyclers.

C&D recyclers in Europe have been utilizing robotic sorting systems in recent years, but many of their American counterparts have skeptically wondered how robots could possibly work here among higher production flows and more varied streams in both size and composition. What quickly became clear was that in order to give the robots any chance of effectively doing their job, the material stream being presented to them had to be radically improved.

To enable their ZenRobotic robots to effectively pick large wood, aggregates, rigid plastics and more on the manual A sort line, the teams at Komptech and Plexus developed a piece of front-end machinery to do just that—an extreme-duty, 14 foot by 20 foot ballistic separator. While its predecessor, the primary vibratory Finger Screen, strictly separated big from small, the ballistic separator allows for a three-way material separation.

The ballistic separator’s aggressively shuffling paddles pass the small- to medium-size fraction through circular holes in its paddles, while carrying the two-dimensional stream (think tarp, carpet, film plastic, cardboard, etc.) up and over the end, while in the process, rolling back the three-dimensional stream consisting of materials such as aggregates, wood and rigid plastics off its opposite end.

Each of these three ballistic-separated streams are collected by conveyors and directed for efficient onward processing with a substantially reduced number of manual sorters needed. With the majority of the bulky trash being directed to the two-dimensional sort line with minimal sorters, the valuable recyclables on the 3D conveyor can now be readily seen and accessed for optimized recovery with a reduced number of sorters either of the human or robotic variety.

The combination of the shredding and ballistic separation action has the added benefit of cleaning up metals, as a powerful in-line magnet can effectively capture large nonferrous metals before the 3D sort line. Another innovation in these systems that helps maximize recovery efficiency and uptime is the use of walking floor trailer-size metering bunkers for the 3D stream. These help regulate the flow to the 3D sort line, which is critical for use with robots, but equally as valuable for human sorters.

Help is on the way

These combined technologies offer respite for sorters, who have long wished for a day where they would only mostly receive good-quality material where they can simply see and pick what they want without being overrun by less valuable materials. The ballistic separator, which typically follows a shredder and vibe pan feeder to help spread out the flow to the far reaches of its paddles, helps make this happen in a way never before seen in North American C&D facilities.

Rather than requiring 10-15 sorters on a high-production manual A sort line, a ballistic separator-based C&D system will more commonly require just a handful of sorters strategically placed throughout. With a more uniform, regulated and stratified material flow, fewer sorters can achieve far higher recovery rates than was possible on less sophisticated lines.

These separators also offer another benefit in the form of negative sorting wood. While it is no secret that wood typically compromises 30-40 percent of the entire waste stream entering C&D recyclers’ yards, it has up to now largely been impossible for sorters to pick everything else off of the line to allow the abundant stream of wood to remain on the belt. But with the ballistic separator mechanically separating the large two-dimensional from the 3D stream, negative sorting of wood on the 3D sort line can now be readily achieved.

Like every piece of technology, ballistic separator-based C&D systems are not for everyone. As these systems are more equipment-intensive (so that they can be less labor-intensive), they tend to be larger and have a higher capital cost (though a lower long-term operating cost). So, we tend to see these gaining strong traction in higher tip fee areas where recyclers have larger daily inbound volumes, higher labor rates and established end markets for products.

While the ballistic separator was designed to optimize the performance of robots, North American recyclers have quickly discovered that it also helps substantially improve the performance of its human sorters and its overall lines. The result is there is little doubt that we will see an increasing number of C&D systems utilizing robots to help out manual sorters in the coming years, which is good news, as there is a place for both—under the right conditions.

This article originally ran in the March/April issue of Construction & Demolition Recycling magazine. Howard Fiedler is the VP of sales at Sparta Manufacturing. He can be reached at Howard.Fiedler@spartaway.com. Sparta Manufacturing designs, manufactures and installs C&D recycling systems.