Making of Pulp Video Lecture | Chemical Technology - Chemical Engineering

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Idaho forests play an important role in
the making of paper and a clear water
paper in Lewiston Idaho wood chips
sawdust bark and other small pieces are
ingredients for paper and electricity
did you know that clearwater paper is
often the number two customer for many
area sawmills making sawmill residuals a
valuable product did you also know that
Clearwater papers mill at Lewiston
accounts for half of all forest product
sales in Idaho more than 240 truckloads
of wood fiber a day arrive at the mill
mostly from Idaho sawmills each truck is
raised to an 80 degree angle and empty
its contents then sorted wood chips and
sawdust will be used to manufacture the
pulp from which paper is made bark and
other small pieces known as hog fuel is
burned generating steam that powers
paper machines at the mill and runs
turbines to generate green electricity
the wood chips are first screened for
sized pieces that are either too big or
too small are returned to the hog fuel
pile shorted chips are then washed and
sent to the digester when delivered the
content of the wood chips is
approximately 50 percent water and 25
percent cellulose fiber the cellulose
fiber is what the mill needs to make
pulp which is the main ingredient used
to make paper the remaining 25 percent
is a liquid called lignin lignin is the
natural glue that holds the wood fibers
together in order to get to the fiber
the first order of business is to remove
the lignin separating this brown colored
material happens in the digesters the
digesters are like large pressure
cookers
the wood chips are placed in this vessel
along with some liquid cooking chemicals
called white liquor the lid on the
digester is closed and steam is
introduced as heat and pressure increase
inside the digester the lignin begins to
dissolve and the wood chips begin to
break down think of white liquor as soap
separating the wood fibers and washing
out the glue or lignin the cooking
liquid
now containing the broken-down lignin is
called black liquor when it leaves the
digester it's very diluted containing a
lot of water the water is evaporated out
concentrating the remaining lignin and
cooking chemicals this mixture is burned
and especially designed boiler called a
recovery boiler which generates steam
and electricity for the mill after
burning all that remains of the black
liquor are the spent cooking chemicals
called green liquor in a final process
lime is added restoring and recycling
the original chemical composition at
this stage the mixture is again known as
white liquor and is ready to begin the
cycle again in the digesters this cycle
of white to black to green and back
again to white cycles again and again
making the process not only
environmentally sound but also very
cost-effective in fact this large
intricate recycling process known as the
craft process is what made paper
affordable to the masses for the first
time in history back at the digesters
the remaining cellulose fiber isn't yet
totally pure and in order to get rid of
any remaining lignin the fiber is
transferred to bleaching stations here
pulp is washed with bleach and water in
a series of steps assuring all remaining
lignin has been removed with each step
the fiber becomes whiter and whiter what
started out as a very Brown dark wood
fiber is now bright white and ready for
use
from here the cellulose fiber or pulp is
either sent to the tissue mill
paperboard mill or to the pulp dryer
where it's dried bailed and stored for
future use water is key in paper making
paper mills use a lot of water the clear
water paper mill uses millions of
gallons a day water is used to cool to
clean and as a way of moving product
throughout the mill water is also used
inside the boilers to generate steam and
help cool machinery water is
continuously recycled throughout the
mill in the end the water is returned to
the river but only after being filtered
cleaned and purified through a very
complex system clear water paper
operates with some of the tightest
discharge constraints of any pulp mill
in the United States today's modern pulp
mills operate as cleanly as possible
much of the equipment which costs
millions of dollars is required to keep
the mill environmentally sound very
little goes to waste and great efforts
are made to truly be good stewards of
the environment
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