Operations Focus: Sizing Things Up

There is no perfect formula that mixed C&D recyclers can follow to determine the best setup of their operations. Knowing the composition and volume of the incoming material and understanding the available end markets are important considerations.

Equipment can vary based on material mix and whether the bulk of material is going toward refuse derived fuel (RDF) or mulch or if it is being further separated.

“You can spend $500,000 or you can spend $5 million, it just depends on what you are getting and where it is going,” says David Whitelaw a Florida-based area sales manager for Komptech USA, Westminster, Colo.

In a construction area where new homes are being built, mixed C&D recyclers take in a majority of new construction waste. In cities, there tends to be more demolition material, says Whitelaw. “Once you figure out what your waste stream is then you can figure out what you are doing with what,” he says.
 

STARTING OUT
In Whitelaw’s experience most mixed C&D recyclers start out separating by hand. Sorting this way it doesn’t take long to figure out the makeup of material that is coming into a facility. Processors can then figure out the percentages of each material in the incoming stream and identify markets for them. From there, they can determine which kind of equipment they will need.

Whitelaw says that in a demolition area, a recycler will need some sort of screen right away to get rid of the fine debris or dirt. “In a new construction area, they wouldn’t necessarily need a screen because they wouldn’t be getting that type of stuff,” he says.

Some end markets involve more sorting, and more sorting can mean more equipment to aid in that process. It can be worth the investment to have more sophisticated sorting operations. Whitelaw points out that RDF pays about $10 per ton. With further sorting, recyclers could retrieve cardboard, which pays about $150 per ton.

The amount of material sorting is dependent on the end market. RDF is a dirtier, coarser product than mulch. Recyclers may get more money from a mulch maker, but the process involves more sorting to keep the wood clean. In a 40 percent wood stream, about 20 to 25 percent may be mulch-grade material, which cannot include any painted, treated or stained wood.

The good news is that, in most cases, the same particle size is suitable whether the wood is going for RDF or for mulch, according to Whitelaw. A 3- to 5-inch product can be further reduced by the mulch producer if necessary.
 

EQUIPMENT NEEDS
As a general rule, trommel screens are placed toward the end of a recycling system, according to several equipment manufacturers. When they are placed on the front, Whitelaw says they take more abuse compared to a flat deck screen. Finger screens and flat deck screens are placed on the front end. These types of screens separate the 10-inch minus from the 10-inch overs. The overs are sent to one picking line, and the 10-inch minus material goes to another.

Trommels can be used for producing mulch or RSM (recovered screened material) at the end. Those that use shredders on the front end produce a lot of RSM because they are breaking material into smaller pieces and creating more fine debris, according to Whitelaw.

If the system incorporates preshredding, a smaller screen size can be used. The screen creates a consistently sized material that goes onto the pick line. Whitelaw explains that instead of workers having to pull a whole pallet off of a picking line, they will instead be pulling a 12- or 18-inch piece, which is easier to pick.

“You end up with a much cleaner product that you are picking and sorting and a higher percentage of recycled material,” he says.

Whitelaw advises that once an operation starts taking in 250 to 300 tons per day, a shredder on the front end is a necessity, because it becomes too difficult to hand sort the material without reducing the size. “That’s just too much material to do that in one day,” he comments.

Whitelaw is currently working with a new C&D recycler in the Southeast. Much of the material processed at this facility is being sent for RDF. He says that initially the operation is not using any screen on the front end because it is located in a new construction area. The recycler is starting out with a regular sort for materials, but once volumes increase, Whitelaw says, the facility will probably install a shredder and a screen and perform a negative sort. In a negative sort, the picking line will basically pull out all the rock, brick, dirt, concrete and steel that cannot be used in RDF.

“Initially, volumes are not high enough to justify those costs yet for a shredder and a screen,” says Whitelaw. Other materials that cannot be burned as RDF include PVC (polyvinyl chloride) and vinyl siding, which emit the pollutant chlorine.

Komptech manufactures a ballistic separator called a Ballistor, which takes the material that is run through a slow-speed shredder and separates the two dimensional material from the three dimensional material. Paper, plastic cardboard go one direction, and all the rock, brick, wood, cans and bottles go another direction.

“What that does is make the picking line even that much more efficient. Because it is run through a shredder on the front end and everything is sized really nice,” says Whitelaw. He adds that magnets and eddy currents work better because the plastic, which he says is the No. 1 problem in the C&D picking line, is not commingled with the metals.
 

END PRODUCT CONSIDERATIONS
Tim Griffing, stationary systems engineer at Continental Biomass Industries (CBI), Newton, N.H., says that most of the company’s customers who produce a mulch product grind the wood directly from the picking line so they only touch the material once. Because of contaminants in the soil product that comes from C&D, Griffing says it is usually used for cover.

“The mulch market is limited in using C&D wood due to local regulations, Griffing says. “Some states allow it. Most don’t,” he adds.

The capacity of the grinder will determine the style and size of screen to be used in the system, Griffing says.

Some C&D recyclers adjust the amount of RDF or mulch they make depending on the time of year or the market that is available to them. CBI designs two wood conveyors positioned under the mezzanine that are bi-directional, so the sorters can pick two different wood products and separate them into two different bins.

“When using a shredder that has adjustable sizing, unlike twin-shaft shredders, the material may be sized to a uniform size and uniform flow to pass over the primary screen.” Griffing adds, “The primary screen can be of different styles, and that is driven by what size the customer needs to screen out.”