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Best Practices in Wood Waste Recycling Click here for printable PDF version Drum
and Trommel Screens Material: Wood Waste
Issue: The
wood waste delivered to a processing facility
typically contains a certain quantity
of small chips, chunks, fines, and contaminants
mixed in with larger pieces of wood waste
causing a number of problems. Small-sized
wood and fines complicates manual sorting
activities with a large number of individual
pieces and hidden contaminants that are
also present on the conveyor. The wood
fines are also typically mixed with dirt
and grit contaminants. The combination
of fines, dirt, and grit causes excessive
wear on material handling and size-reduction
equipment, thus creating excessive equipment
maintenance requirements. Finally, the
small contaminants can be missed by manual
and automated contaminant removal systems.
Failure to remove these small contaminants
can lead to excessive equipment maintenance
requirements and degrade the quality of
the end-product.
Best Practice: This Best Practice recommends the removal of small sized wood, fines, and small contaminants from wood waste at the front end of a processing facility using a drum or trommel screen. This type of screen consists of a large, revolving cylinder that is sheathed with a screen. The cylinder is positioned with a slight slope so that material that is loaded into the upper end of the drum will be gravity fed through the cylinder as it turns. As the wood waste travels the length of the cylinder, small material falls through the screen onto a conveyor below. The screen openings are carefully sized to remove material of a targeted size. The acceptable material passes through the cylinder onto another conveyor for further processing.
Implementation: Drum or trommel screens should be installed in the initial stage of wood waste processing to remove small materials and contaminants early in the process. The selection consideration issues for a drum or trommel screen include:
Operational. By working with an equipment vendor, drum or trommel screens can be sized to handle types and volumes of wood waste processed at a given facility. Drum or trommel screens can be effective if sized correctly (i.e., if they are with enough to present adequate screening area and long enough to provide an adequate material retention time). Units are typically loaded at a maximum of 40 percent of their diameter. As the drum rotates, the screen opening expands from ‘0’ at 45 percent to a maximum at 90 degrees, again decreasing to ‘0’ at 135 degrees. This requires a larger screen opening to ensure efficiency and affect the diameter of the drum. A portion of fines can be entrapped in the material bed, requiring multiple drops during rotation to increase the possibility of the fine material passing through a screen opening. This factor affects how long the materials must remain in the drum.
Maintenance. Drum or trommel screens are very effective if the material is dry, but have a tendency to plug up and require maintenance when processing wet material. However, users find that trommels handle wet material better than vibrating or gyratory screens.
Cost. These screen systems are relatively expensive compared to competing screen systems and require a significant amount of space.
Safety. The operation of drum or trommel screens can create a significant dust problem.
Benefits: Removing small wood, fines, and small contaminants during the initial stage of waste wood processing can effectively remove contaminants and reduce equipment wear. Drum or trommel screens are an effective piece of equipment for removing small wood, fines, and small contaminants such as metal, rocks, and glass from the larger pieces of wood waste.
Application Site: Processing Facility.
Contact: For more information about this Best Practice, contact CWC (206) 443‑7746, e-mail info@cwc.org. References:
1.
General Kinematics;
equipment brochure 2. Lyman, Mark. West Salem Machinery. Salem, OR.
3.
Sherman, Raymond.
General Kinematics; Barrington, IL. (See Appendix for an Equipment Manufacturers List)
Issue
Date / Update:
March 1997
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