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Best Practices in Wood Waste Recycling Click here for printable PDF version Process Modifications for Wood Waste Feedstocks Material: Wood Waste
Issue: Pulp and paper industry were originally designed and constructed to use virgin wood feedstocks as a raw material. Some of the virgin wood fiber used for the pulp and paper industry is from lower value roundwood logs that are chipped for pulping. The other major source is from the residuals from sawmill, veneer, and lumber plants. These solid wood production plants produce millions of tons a year of residual barks, chips, and sawdust that they cannot use but can be used for pulping. This wood fiber is too small, or too defective for solid wood manufacturing. The remaining virgin feedstocks are typically derived from the residual chips produced by primary wood products manufacturers (sawmills and plywood plants) that rely on the round log for their raw material. The virgin wood fiber is generally free of non-wood contaminants and relatively uniform in specie, geometry, color, and moisture content.
The
feedstocks
produced
from wood
waste
for the
pulp and
paper
industry
are more
complex.
They
frequently
contain
various
quantities
of non-wood
contaminants,
consist
of a number
of different
species
(softwood
and hardwood
varieties),
lack uniform
geometry,
include
weathered
wood colors,
and might
vary significantly
in moisture
content
(green
wood to
kiln dried).
These
complex
characteristics
are a
challenge
for the
pulp and
paper
industry
because
their
production
systems
were not
originally
designed
to account
for these
feedstock
variations.
Best Practice: This Best Practice recognizes the special challenges presented by wood waste feedstocks. Therefore, this best practice recommends the implementation of certain process modifications at pulp and paper mills when substituting wood waste feedstocks for a portion of the raw material supply. These techniques allow the manufacturer to maintain full control of the wood waste material as it enters into their production process.
Specialized
Quality
Control
System.
The
use of
wood waste
feedstocks
require
the pulp
and paper
mill to
adopt
specialized
feedstock
sampling
and analysis
techniques
to maintain
adequate
quality
control
of their
wood waste
supplies.
The
wood waste
feedstocks
require
a greater
amount
of monitoring.
The quality
control
system
should
account
for the
presence
of non-wood
contaminants,
unique
feedstock
geometry,
and variable
moisture
content.
The
pulp and
paper
mill should
customize
their
feedstock
specification
for the
wood waste
material
complexities
and variability. A workable sampling system for accurate monitoring
should
be developed.
Since
a single
delivery
of wood
waste
feedstock
could
contain
significant
variations
within
the load,
multiple
sampling
might
be necessary
to attain
an accurate
quality
assessment.
Segregated Storage System. Wood waste feedstocks should be stored separately from the conventional feedstocks. Segregated storage allows the pulp and paper mill to employ additional contaminant removal techniques, maintains close control of mixing with conventional feedstocks, and restricts the wood waste from certain product lines, if necessary.
Enhanced
Contaminant
Removal
Systems.
Wood
waste
feedstocks
might
require
additional
cleaning
before
use. Therefore, the pulp and paper mill should consider
enhancing
their
contaminant
removal
systems. Possible contaminant removal systems include: magnets for ferrous
metals,
air density
separators
for hard
contaminants
(e.g.,
non-ferrous
metals,
rocks,
and glass),
air density
separators
for soft
contaminants
(e.g.,
some light
plastics,
paper,
cloth,
and StyrofoamŪ),
and chip
washers
for dirt
or grit.
Removal
of soft
contaminants
are the
least
developed
techniques.
Effective
contaminant
removal
systems
would
also allow
the pulp
and paper
mill to
blend
higher
percentages
of wood
waste
materials
into their
process
without
compromising
product
quality
and minimizing
processing
difficulties.
Controlled Blend with Conventional Feedstock. The pulp and paper mill should have a separate material handling system for the wood waste feedstocks to meter the material into the production process at a controlled rate. The waste wood feedstock is less likely to cause manufacturing and end-product problems when it is blended with the conventional feedstock. In the absence of an accurate metering system, the pulp and paper mill run the risk of allowing a spike in the percentage of wood waste feedstock. This could lead to problems with processing equipment or the end-products.
Implementation: The substitution of even a portion wood waste
feedstocks
for conventional
virgin
wood feedstocks
in a pulp
and paper
mill is
complex.
The
pulp and
paper
mill need
to assess
the inherent
complexities
of waste
wood feedstocks
and customize
a segregated
system
for using
this material
into their
existing
process.
Capital
investments
to modify
the raw
material
preparation
equipment
at the
front
end is
required
to properly
prepare
wood waste
feedstocks.
The
pulp and
paper
mill should
work closely
with wood
waste
suppliers
to understand
the quality
characteristics
of the
alternative
feedstock
and then
adopt
appropriate
process
modifications
to neutralize
any adverse
characteristics
of the
raw material.
Benefits: The implementation of certain processing techniques at pulp and paper mills would allow for the substitution of wood waste feedstocks for a portion of their raw material supply. The ability to process wood waste feedstocks helps control raw material costs by expanding the raw material base and sourcing flexibility of the pulp and paper mill. Under certain fiber market conditions, this sourcing flexibility is extremely advantageous in keeping raw material costs as low as possible. The capability to process wood waste feedstocks also anticipates possible future shortages in the supply of virgin wood feedstocks.
Application Site: Processing Facility. Contact: For
more information
about
this Best
Practice,
contact
CWC (206)
443‑7746,
e-mail
info@cwc.org.
References: 1. International Resources Unlimited, Inc. Eugene, Oregon. 2. Smith; David. CE/Western Engineering. Albany, Oregon.
Issue
Date /
Update: March
1997
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