A recycler never knows what he or she will find in a construction and demolition (C&D) debris container. Every load may contain a surprise, making it more difficult to recycle. That’s why creating guidelines and supervising incoming material is essential for businesses. Most try to keep nonacceptable items out, but it has become a common problem for many facilities. With ever-changing types of material ending up in C&D loads, it’s vital to select the proper recycling equipment.
Waste composition, collection and transportation methods may vary across the country. Transfer stations tend to compound the problem, and clients are usually more concerned with construction schedules than with taking time to recover packaging materials from the job site. Everyone has deadlines and budgets to keep, but the effectiveness of recycling programs and seasonal changes may limit the ability to capture certain materials.
No matter how careful a recycler is, the value of certain materials is diminished when exposed to others. To improve the material stream, a recycler has to ask the following questions: Can the material in question be sorted and kept clean? Is it a struggle to process different material streams with the same system? Am I looking to add or eliminate presort stations? Does the primary screen capture all the fines material, or do fines ride on top of larger items and surf across the screen?
Regardless of the material being processed, screening solutions have become an important component of every recycling system.
SCREEN PERFORMANCE AND RECOVERY RATE
Screen performance has a tremendous impact on the recovery rate of C&D debris. Conventional screening methods, such as trommels or star screens, have limitations, while new dynamic disc screens are designed to prevent clogging and wrapping issues that occur with conventional screens. Dynamic disc screens make it easy to adjust the screen size for different types of materials. In terms of versatility, capacity and footprint, a dynamic disc screen is a much more efficient solution.
Vibratory and rotating drums that have the same capacity will require two to three times the footprint. The Eco-Star screen by Aggregate Equipment Inc., Leola, Pennsylvania, for example, has rotating shafts that constantly flip the material and capture the smaller items. Film and plastics tend to float above the flat discs. The remaining items discharge off the end of the screen in a metered flow to enhance further separation. The screen is designed so product sizing and efficiency remain constant.
It’s been noted that successful recycling operations handle debris fewer times than other systems and use effective screening methods to separate the stream by size. The quality of the screening process determines the efficiency and performance of subsequent processes, such as ferrous metals recovery, density separation, manual sorting/inspection and volume reduction. If the fines aren’t removed by the primary screen, chances are the sorted products are contaminated. Any remaining fines and debris on the final sort belt typically end up in a landfill as waste. In that case, the fines content doesn’t matter.
But things are changing, and many C&D recyclers are finding ways to divert the residuals from the landfill by creating an alternate fuel product. In these instances, getting all the fines out becomes a higher priority.
The sorters and automated processes focus on capturing recyclables and removing contaminants to improve the quality of the fuel product. With the negative sort process, all materials that remain on the sort belt are transformed with size reduction technology and screens to produce alternative fuel. If the fines remain on the belt, the contamination level may exceed alternative fuel quality requirements, which is why the efficiency and performance of the screening process is crucial. Proper sizing and recognition of material is vital to improve the effectiveness of automated and manual sorting.
When markets tighten up, suppliers of quality products will outperform the competition. Contamination and purity levels are directly related to screens and secondary sorting methods. To produce high-quality, low-impurity commodities, equipment must be properly selected; however, properly recovering materials from the waste stream is an expensive proposition. The markets fluctuate and the intrinsic value of recovered items are less than the dollars spent capturing them.
It’s risky to stockpile large quantities of sorted materials and hope the markets will improve. That’s why it’s important to capture the items that are profitable.
Constantly evaluating performance and maintaining equipment can reduce downtime and improve the bottom line, but the key is investing in the right equipment in the first place.
Explore the March 2018 Issue
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