Built to move

In a material recovery facility (MRF) or mixed waste sorting facility, a conveyor system is the lifeline of efficient material handling. A well-thought-out conveyor system designed around a facility’s specific requirements improves productivity and safety.

To ensure the conveyor system is adequate for material handling needs, owners often work with systems suppliers or original equipment manufacturers to design a custom conveyor solution as part of the sorting system.

Not following the rules of conveyor system design can lead to significant issues, says Alex Wolf, director of technology at Van Dyk Recycling Solutions, a Norwalk, Connecticut-based systems supplier that works with operators running everything from residential and commercial single-stream to municipal solid waste (MSW) or construction and demolition (C&D) debris.

“I’m managing the design team here with seven design engineers, and we have a lot of rules that they have to follow on how you arrange those conveyors together, and there’s a lot of factors and widths and keeping certain clearances [involved],” Wolf says. “If you don’t do that, the operator is going to feel the pain. If you’re not designing this correctly, they’re going to get a system that’s just going to frequently jam—that is not keeping up with the capacity.”

Careful conveyor design can prevent loss of productivity caused by those issues, says Wolf, who explains that a lot of science goes into proper conveyor design.

Designers typically approach each conveyor system project as a custom solution for a customer’s individual needs, choosing the right pieces of equipment and conveyor types to use in each given application within the plant, says Brad Goins, sales engineer for Machinex Technologies, a Québec-based systems integrator and manufacturer that builds equipment for many of the biggest names in the waste handling arena, from single-stream recycling plants to MSW processing systems to source-separated organics facilities.

Design process

The conveyor selection process is driven by what the operator is processing—whether it’s single-stream recyclables, C&D materials, MSW or aggregates—as well as where within the system the conveyor will be located. Additional factors considered in the design process include processing capacity, labor requirements and more.

After completing an inbound materials study to determine input composition, the Van Dyk design team compiles all pertinent details into a flow chart before executing the design proposal, Wolf says. Most of Van Dyk’s customers are looking for a highly automated system to reduce manual labor, he says.

When designing a system, Goins says his team is not only thinking about the conveyors but concurrently about all of the processing equipment within the MRF. He also considers the products that will already have been separated by an optical sorter or ballistic separator, for instance, to determine the most appropriate type of conveyor for the facility.

Goins says it’s important to standardize common wear parts, including gears, motors, bearings, heads, pulleys or belting material, to simplify repairs and lessen the burden on customers.

“They’re one of the key pieces that can keep a MRF up and going, and having standardization of parts throughout the MRF can help the operation be more efficient with keeping that facility up and running,” Goins says.

While the conveyors themselves are not typically custom-built, the system design is a custom solution for each customer, he adds.

“A lot of the conveyors that we build, they’re standardized pieces of equipment, but the links may change. The widths may change, the speed of the belt, the belt pipe, depending on [if] they’re a flat conveyor or an incline conveyor to a certain angle,” Goins says.

These variables can come into play when adapting a conveyor system to a certain application, he adds.

Anatomy of a conveyor

Various types of conveyor systems come with advantages and disadvantages. A number of conveyor types are most commonly used in single-stream recycling and waste-sorting facilities:

Chain roller conveyors—These robust conveyors include a belt assembly and chains running on rail-type tracks. They can be designed with different pitches and typically are used in heavier-duty applications, such as on the front end of a plant as part of the infeed application into a recycling facility.

Slider bed conveyors—Designed to process lightweight materials and recyclables, these conveyors often are used to handle less abrasive material.

Conveyors come in varying frame constructions, including closed frames typically used for slider bed conveyors that handle fewer abrasive materials, and open frames typically used during the processing of glass and abrasive materials.

Machinex also offers custom-engineered side panels or sidewalls that can be adjusted depending on the product to be conveyed as well as the angle and speed of the conveyor.

Understanding the stream

Conveyors essentially are sorting systems, so it’s imperative to consider the type of materials being conveyed and the changes in material throughout the stream. Whether operators are sorting something abrasive such as glass or something light such as flexible packaging will determine whether they need heavy- or light-duty conveyors, Wolf says.

Single-stream facilities will require a different conveyor setup than mixed-waste facilities. Input is more controlled in a single-stream facility, Goins says, and the material stream typically won’t contain as many products that could harm the belt as might be found in a mixed-waste environment.

While the front-end conveyor process is fairly similar in both settings, incorporating roller chain conveyors for a presort farther downstream can differ. In a single-stream MRF, different commodities are separated from the stream, so the further into the system, the less robust the conveyors will need to be.

In an MSW facility, on the other hand, the system typically will begin with a roller chain conveyor and move to a slider bed and slider roller, Goins says, with robust belts throughout.

“You’re going to stay a little bit more robust within that design, just for the simple fact that there’s a lot more unknown within an MSW process than a single-stream,” Goins says.

Biggest challenges

Both Goins and Wolf agree that when designing a sorting system, space is always the biggest challenge.

“When you design a sorting system, space is always a challenge. It’s a space puzzle, basically,” Wolf says. “In many cases … we have a very small space, and then it becomes challenging to fit everything in there and make it work at the same time.”

Most of the systems will go into existing facilities where space is at a premium, Goins adds.

“You have to [consider], to get from one piece to another, what do I need to do to be able to maximize the incline of that? Curve ups or curve downs within the conveyor potentially would need to be designed,” he says.

Designing transition points between one conveyor to another can be challenging, as well, as ensuring you have enough height or drop to manage the material being conveyed without causing issues with potential jams is critical.

Limiting spillage points is a top priority, Goins says, so operators should ensure scrapers and belt cleaners are placed correctly over the conveyor to limit potential spillage and keep the facility as clean as possible.

Safety is another top concern, and working with an engineering team can help ensure conveyor systems are compliant with U.S. Occupational Safety and Health Administration regulations, including safety guard, belly pan, tail guard and head guard requirements.

“It’s making sure that sorters or other personnel that may be working around those conveyors can’t get into the dangerous areas of the conveyor,” Goins says.

Maintenance requirements

Regular maintenance is crucial to keeping a conveyor system running reliably. Bearings need to be monitored, as does the temperature of the motor to extend motor life, Wolf says. Goins also recommends making sure return rollers are cleaned regularly and ensuring belts are equipped with scrapers.

Conveyors are the lifeblood of a MRF, so inventorying spares of those commonly replaced items is recommended, Goins says.

Machinex designs its larger conveyors with the ability to remove the head fully without having to break the belt, and Van Dyk likewise focuses on making conveyor systems accessible so the operator easily can maintain the system.

“Most of our customers move far beyond 4,000 hours per year of operating time, and they get constantly pounded with material,” Wolf says.

“The average car wouldn’t last a year if you put that kind of mileage on it. Compared to that, conveyors are actually pretty low-maintenance items for the most part.”

The author is managing editor of Waste Today and can be reached at smann@gie.net.