The fibre is delivered to the pulp mill by
an efficient conveyor system, where it is
dumped into spherical cookers, called di
gesters. Water and alkaline chemicals are added,
the cover bolted on and the digester rotated.
After rotation starts, steam is allowed to enter the
digester in order to digest the encrusted materials
away from the cellulose fibre. Rotation helps mix
the chemicals with the flax so that uniform di
gesting results. At the end of the prescribed
cooking cycle the digester is relieved of its pres
sure and the pulp dumped into a channel through
a large hopper. Specially designed pumps take
the pulp from the channel and deliver it to the
next stage of the process—the washing and beat
ing operation.
The digested stock is pumped into large break
er beaters, each beater holding a complete cook.
The fibre is worked underneath a heavy rotating
roll to break it down into shorter lengths. At the
same time large quantities of fresh water are
added which displaces any of the alkaline solu
tion remaining. In this way all the dissolved en
crusting materials are removed, leaving the brown
fibre.
The stock is then pumped from the breaker
beaters through a continuous chlorinating device.
Chlorine is added to the fibre as it passes through
the pipe line. In order to use the chlorine as com
pletely as practicable, a retention chest is pro
vided for the reaction to continue to the desired
limit.
After the pulp is chlorinated, it is neutralized
with alkaline materials and washed on rotary
vacuum washers. By chlorinating in this manner,
some of the brown coloring matter becomes solu
ble when extracted with alkali. The pulp is then
bleached with hypochlorite bleaching liquor to
make it white and to remove the last traces of
the encrusting materials present. This operation
is closely controlled in order not to degrade the
fibers beyond a certain point. In order to obtain
a uniform product viscosity determinations, a
measure of chain length, are made while the
bleaching reaction is going on. The reaction is
stopped by dilution with large volumes of water
at the proper point and the residual bleach liquors
are washed out. This washing operation is also
carried out on rotary vacuum washers. The resul
tant fibres are then a pure snow white pulp. This
pulp is conveyed from the pulp mill to the bleach
ed pulp storage and stored in boxes for use in
the paper mill. The boxes are drawn from the
pulp storage as needed in the Refining Room.
One of the 12 breaker beat
ers in which the fibres are
shortened and the remaining
alkaline solution is washed
out.