When you are looking to retrofit your existing system, make sure that you look at all aspects of the sorting process and prepare the material for separation success.
By Mark Neitzey
Images courtesy of Van Dyk Recycling Solutions.
In my role as Director of Sales, I have traveled North America week in and week out visiting MRF operations all over. I see first-hand the challenges that these sites face. I see highly contaminated inbound material streams and inbound stream changes (such as lightweighting, the Amazon Effect, reduction of ONP, and the increase of film and trash). I see high maintenance costs and increasing end product quality demands. I see challenges in maintaining a safe working environment. I see a multitude of sorter labor issues (simply finding willing candidates to show up every day and dedicate themselves to sorting through trash at 50 picks per minute for minimum wage is a challenge). Today’s MRF is feeling the brunt of the squeeze.
I field questions in my travels from operators who are looking for quick and permanent solutions to these issues. Questions such as:
• Can I just drop in an optical sorter to make a “China spec” grade?
• My temp labor service can only supply me with 14 sorters today, but I need 22 to run at capacity—and its worse on the second shift. Should I get robots instead?
• Can my system change its settings (conveyor speeds and screen angles) based on the inbound stream that I am receiving?
Whatever the technology that you are considering—and there are some really cool machines out there (robots, optical sorters, material monitoring cameras)—you must remember that the material first needs to be properly prepared before it can be properly recognized and sorted (or even monitored) by an intelligent sorting device. Any separation device—a screen, an optical sorter, a robot—likes to be fed a steady diet of consistent material all on a single layer of the feed conveyor. If possible, consistent by size with fines removed, similar by shape, rigidity and density.
Luckily, there are several ways to prepare material for intelligent sorting. Here are five things to consider for your system before just “dropping in an optical sorter or robot” into your next retrofit.
#1: Sizing Screens that Do Not Wrap with Film
Mechanical screens are still an important piece of the puzzle at an MRF to help screen and separate material into different fraction sizes. They size the material into different size fractions for further sorting or intelligent separation. Large fractions and fines can be removed, and a target size can be directed to an intelligent separation device (like an optical sorter or robot). In the last few years screens have been greatly improved. Many suppliers now offer non-wrapping screens that properly size material without allowing film bags to wrap around their shafts.
Image courtesy of Westeria.
#2: Elliptical/Ballistic Separators
An elliptical or ballistic separator is not unlike the elliptical machine that you might see at your gym. Striding paddles walk two-dimensional objects over the screen (items like film bags and light sheet paper). Rigid items (bottles, cans, 3-D cardboard) bounce back. Also, the paddles have true 2-inch holes in them to allow the last bit of glass fines to fall through. With minimal maintenance and no star changing required, the elliptical separator has clearly overtaken the role of a final clean up commingled or polishing screen at an MRF. With its ability to remove light sheet paper and film and remove fines, it is becoming a must-have to properly prepare your container line for further processing (whether that is optical sorters, robots or even humans).
#3: Conveyor Belts (Speeds, Angles, Widths, Sequencing, Proper Cleats)
Conveyor belts and sequencing play a large role in the success of any intelligent separation device. Why? The goal is to get the material to a single layer to give the separation device a chance to succeed. Setting two consecutive conveyors to operate at different speeds can help thin material out. Whenever possible, feed subsequent conveyors in line, instead of at 90-degree angles. This will help spread material. Using wider transfer conveyors prior to the separation device can also help. Proper cleats on inclining conveyors will break up material and keep it from clumping together. Having all the conveyors on variable speed drives to give maximum flexibility to properly sequence the conveyors can help. These are all small details, but they all play a part in properly preparing the material for intelligent separation.
#4: Vibratory Feeders and Disc Spreaders
If the system has the extra height needed, a vibratory feeder or a disc spreader could be the perfect tool to help spread the material across a wide belt for single layer coverage to an intelligent separation device. If a customer is buying an 8-foot wide optical sorter, but the incline conveyor that is feeding the 8-foot wide acceleration conveyor is only 4 feet wide, this could be a problem. Only 50 percent of the optical is being used. The vibratory feeder or the disc spreader helps spread the material as it drops on the full width of the optical sorter’s acceleration conveyor.
#5: Wind Tunnels
The addition of a wind tunnel to an optical sorter’s acceleration conveyor is a good way to help process light materials at a higher throughput. Light sheet paper and film starts to fly up and drift when a conveyor speed approaches 550 to 600 feet per minute. A wind tunnel added to an acceleration conveyor applies air flow at the same speed as the conveyor to stabilize the light floating materials and allow the acceleration conveyor to operate at higher rates of speed (upwards of 800 to 1,200 feet per minute). This allows more throughput to pass under an optical sorter and still be at a recognizable single layer.
Prepare for Success
When you are looking to retrofit your existing system, you need to consider these and other factors as part of your added technology. The goal should not be to just drop in a new robot or optical and expect it to single handedly solve all of your problems. The goal should be to look at all aspects of the sorting process and prepare the material for separation success. | WA
Mark Neitzey is Director of Sales for Van Dyk Recycling Solutions (Norwalk, CT). Mark has been involved in more than 100 recycling equipment projects in the last 17 years, including: simple roll cutting and baling sites, large baling systems, wood waste screening, C&D sorting systems, an automated MSW/fuel system, commercial sorting systems, PET/Plastics sorting systems, various single-stream sorting systems and system retrofits. Mark lives in Houston, TX and travels throughout North America, gaining a broad perspective on the industry and its current trends. He can be reached at (203) 967-1100 or e-mail [email protected].