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Mechanical Separation
Techniques Using Conveyors
Material: Wood
Waste
Issue:
As wood waste material travels through a processing facility on conveyors,
it can form layers,piles, or clumps. These layers, piles, or clumps often
bury or hide embedded contaminants (ferrousmetals in particular), reducing
the effectiveness of contaminant removal systems. Failure to remove metalcontaminants
can cause a number of problems such as excessive wear, damage to equipment
in theprocessing facility itself, and contamination, creating problems
in meeting end-user specifications. If thematerial is manually sorted
either for removal of various types of contaminants or for separation
intosub-streams, embedded contaminants and deep piles can also create
problems.
Best Practice: This best practice recommends the integration of mechanical features into conveyor systems that will improve the exposure of contaminants to specialized removal systems (especially ferrous metals) and to manual sorters. Distribution and exposure of the material flow also helps sorters separateinto various sub-streams.
TYPES OF MECHANICAL SEPARATION TECHNIQUES
Mechanical Waterfalls or Cascades: These types of conveyor designs allow
the wood waste material to fall and tumble during exchanges between conveyors
and equipment. This dynamic transfer has the effect of redistributing
the material on the conveyor and exposing previously hidden contaminants.
Since optimal fall distance arrangement depends on the flow volume and
size of the conveyed material, so some experimentation may be necessary
to fine-tune the system. A series of waterfalls followed by magnets greatly
improves the effectiveness of metal removal.
Staggered Conveyor Speeds: Another technique in redistributing wood waste
on a conveyor is to transfer the material from a low speed to a high speed
conveyor. This transfer has the effect of spreading out the wood waste
into a thinner layer that is easier to clean by magnetic cleaning systems
and to sort manually.
Baffles or Screens: Baffles or wide opening screens positioned at a waterfall
or cascade between conveyors
can be used to redistribute the wood waste material on the conveyor. This
equipment jumbles the waste
wood material more than the waterfall alone.
Implementation:
These types of mechanical conveyor arrangements can be designed into existing
and green-field wood waste processing facilities to improve the effectiveness
of metal contaminant removal systems or manual sort lines. The configuration
of conveyor systems, availability of processing space, and prevalence
of contaminants determine which arrangement is most appropriate for the
facility.
Benefits:
The integration of mechanical separation designs in conveyor systems will
improve the ability of magnetic systems to remove metal contaminants from
a process flow of wood waste. If the equipment precedes a manual sort
line, it can redistribute the material onto the sort line in a more exposed
and accessible configuration. The improved removal efficiency will raise
the overall quality of the finished product and allow the processor to
realize higher product sales values.
Application Site: Processing Facility.
Contact:
For more information about this Best Practice, contact CWC (206) 443-7746,
e-mail
info@cwc.org.
1. References:
2. Horne-Brine, Preston; Clean Washington Center; Seattle, WA;
3. Sargent, Bob; Rainier Wood Recycling; Kent, WA;
4. International Resources Unlimited, Inc.; Eugene, OR;
Issue Date / Update: March 1997