1.
Fiber supply:
Our fiber supply consists of three sources: wood chips
of Northwest softwood species, sawdust, and old
corrugated containers (OCC). The majority of our wood
chips and all of our sawdust used as raw materials are residuals
from sawmills or the lumber industry. The wood
chips, sawdust, and OCC must be processed to obtain
individual fibers for papermaking.
2. Kraft Pulping:
Sawdust and wood chips are cooked using the kraft pulping process. White
liquor (an alkaline chemical solution) and steam are used to dissolve
the lignin, the glue that holds the individual fibers together. This is
accomplished in digesters, which are like large pressure cookers. The
sawdust is cooked in a continuous digester in which sawdust, white liquor,
and steam are added continuously. Sawdust pulp is continuously discharged
from this digester. The wood chips are cooked in batch digesters, where
the chips and white liquor are added at the start of the cooking process.
Steam is added to cook the chips throughout the batch, and the pulp is
discharged at the end.
The pulp
is processed through brownstock washers, which separate the used chemicals
from the pulp fibers. The chemicals are then sent to the chemical recovery
process so that they may be reused in the digesters. The washed pulp is
processed through screens to remove any oversized debris before the high
quality fibers are sent to storage for market pulp or papermaking. We
have two separate lines of washers and screens. One line processes only
batch pulp from wood chips for sale as market pulp, while the other line
processes a combination of batch and continuous pulp for papermaking.
3. OCC Pulping:
The old corrugated containers are processed in the OCC Plant. This is a
recycled pulp mill that uses a repulper to separate the cardboard back
into individual fibers, centrifugal cleaners to remove contaminants by
weight, and pressure screens to remove other contaminants by size. Clean
OCC pulp is then stored for use in papermaking.
4. Market Pulp Forming, Drying & Finishing:
For
market pulp, the cleaned pulp is sent to a pulp former and then sent to
a pulp dryer, where most moisture is taken out of the pulp. The pulp is
spooled onto a reel, cut, and baled for shipping. We also keep a portion
of every lot of pulp for testing.
5. Stock Prep for Papermaking:
Most of the Port Townsend Paper's pulp is used to create paper on
site. In stock prep, kraft pulp is refined to make it more flexible and
blended with OCC pulp. The blended pulp is processed through centrifugal
cleaners to remove any remaining contaminants by weight and a large volume
of water is added to prepare the pulp slurry for papermaking.Additives
may also be introduced, according to customer specifications..
6. Paper Forming, Drying & Finishing:
The pulp slurry is fed into a Fourdrinier machine where the slurry is
deposited onto a wire to form a sheet, and the slurry begins to dry. The
sheet is then pressed to further remove water using felt as a blotter
and a series of heated paper dryers. It is then rolled smooth through
metal drum rollers (calender stacks) and then spooled onto reels. The
paper is next cut and finished according to customer specifications. We
take samples of our paper to test for desired properties according to
the grade.
Uses
of kraft paper
Our kraft paper is
used for containerboard and corrugating medium for boxes, paper bags,
paper moving pads, gumming kraft for paper tape, paper trash bags, laminated
roll wrap for fine paper, polycoated products for lumberwrap, protective
papers for construction and painting, envelopes, raisin trays, and padding
for industrial packaging. Our kraft pulp is used primarily on the surface
of linerboard for box manufacturing in Asia. The pulp adds strength, quality,
and a better printing surface to the linerboard.
To
learn more...
Visit the "Paper
University" of the Technical Association for the Pulp and Paper
Industry (TAPPI). You can also contact us about visiting your school or
organization. You
may contact us via our feedback form, call
us at (360) 379-4224, or e-mail us at community_relations@ptpc.com.