The Chronicle-star combined with the Moss Point advertiser., 1948-06-11
Paper Making.
CONTINUED from Page y

chips. The racket near the chip
pers is equal to the din from the
barking drums. The chips drop
on conveyor belts headed for the
digester room, but first they are
screened for size. Great care is
necessary to have the chips within
certain dimensions: Too small a
chip will suffer in the subse-
ouent treatment and lack
strength, while the oversize chip
will be raw in the center and con-
seouently is worthless unless
further processed. To prevent this
the oversize chips are re-cut TO
the right size. The discarded un-
dersize chips 60 to the boiler.
furnaces for fuel.
Digesssrs First Step
In the digester house the chips
come pouring along the conveyor
TO the top, which may be six sto-
ries high. They drop into chip
storage bins atop as many
as 20 digesters. At regular inter-
walls chips are permitted to fall
from the bins into the digesters
for cooking under pressure with
chemicals and water.
The digesters are giant pres
sure cookers usually about three
stories high and 10 feet in diam
efer. They work on the same prin-
ciple as any housewives pressure
cooker. The chips are the main
dish, TO which are added water
and a white or yellow liquor COM
posed principally Of sodium hy-
droxide and sodium sulfide. The
white liquor dissolves the nom
fibrous constituents in the wood
chips, principally lignin and 9TH
er bonding components, natures
way of holding wood cellulose
fibres together. The mixture in
the digesters stews away for 90
minutes or longer under a pres
sure usually of ITO pounds Of
steam per square inch.
After the cook, the chips r re-
leased when an operator turns a
valve. The mixture bursts into
cyclone separators, which r
blow tanks about the size of the
digesters. Pressure behind them
and the effect Of the chemicals
free the wood cellulose fibres
from resins, iignin, and other
natural binders, and blows the
cooked chips apart into a spongy
mass of pulp-strong, tough, Pill
able wood cellulose fibres. While
the fibres are thus separated, they
are not cut off, but retain their
longitudinal character. 1t Is the
longitudinal character that inn
parts strength to Kraft paper and
board.
Treated In Diffusers
The pulp mix, with water and
chemicals still present, passes
from the CYCLONES into diffusers
or into brown stock washers. The
diffusers are tanks in which the
pulp Is thoroughly treated with
water to wash off the chemicals
which are reclaimed. Similarly,
the brown stock washers. the most
modern equipment, pour water
on the pulp. carry 1t over a fine,
rotary wire-mesh through the
pores of which excess water and
chemicals are drawn off the pulp
by suction.
The water and chemicals re-
moved in the diffusers or brown
stock washers is spent cooking
liquor. Known as "black liquor"
the solution amounts in some
mills to several million gallons
daily, and constitutes a hot, dark
brown. soapy, foamy liquid which
contains, besides the soda chem
icals, pitch and rosin and lignin
extracted from the wood. The
idea Is to recover the soda and
sulfur dissolved in this tremen-
dous quantity of liquid in the
most economical way and also
to recover, for economic use, the
component parts of the tree not
used as pulp.
In q continuous process, involv-
ing the capture and reuse of re-
acting chemicals, some of the ma
terial is always lost and must be
replaced to keep the system in
balance. Long ago, when pulp was
first produced by cooking with
lime or caustic soda, a search was
made for a cheap, reliable chem