Chemical Process Industries

1. PULP MAKING
Prepared by- Mr. Vishal B. Thakare
(M.Tech, Chemical SVNIT Surat)
Assistant Professor PARUL UNIVERSITY
Vadodara
vishalbt88@gmail.com

2. Pulp Manufacturing
 Pulp is a commercial fibrous material obtained from bamboo, wood,
bagasse(waste material) etc. by mechanical and chemical means.
 Pulping means disintegration of bulky fibrous material to small
fibers.
 There are mainly three modes of production of pulp:
(a) Mechanical
(b) Chemical
(c) Semi chemical

5.  Logs with bark are debarked by tumbling and rubbing action, then
conveyed to chippers where large rotary disks with many heavy
knives reduce the wood to 2-5 cm flat chips.
The chips are metered via star valve to a deaerator-preheater.
After several minutes, the chips are discharged through a rotating
tapered plug into the lift line where recirculating digestion liquor at
12 atms get contacted.
Transfers chips to the upper soaking zone of the 25-30 m tall digester
tower where lignin and other non-cellulosic content digestion is
done at 170oC and about 1.5 hr.

6. Cooking liquor is withdrawn as side streams and circulated through
external heat exchangers to reheat and control the digestion
temperature within the tower.
The digested chips are cooled to 65oC at the base of the tower by
injection of cold black liquor. This is to avoid mechanical weakening
of fibers from steam explosion of the hot liquor when passed through
the blow-down valve.
The pulp liquor slurry is passed through the valve to a blow tank
where residual heat is recovered in the form of steam which passes
overhead with turpentine vapor to the chip preheater.

7. The pulp is filtered to separate black liquor and screened to remove
wood knots and other undigested residue.
The brown pulp goes either to product finishing operations or to the
bleaching plant.