paper and pulp processing

PAPER AND PULP PROCESSINGJeffrey Joseph Fernandez

Gerffrey Chua

Paper and Pulp paper and pulp --conversion of cellulose

to paper products consumer of large quantities of chemicals largest energy user energy intensive

Raw Material cotton and linen ---> fibers from wood deciduous (hard) and coniferous (soft)--

prefereed because the fibers are longer

Bark - not fibrous and diificult to bleach

Abrasive Debarkingabrasion of the bark due to friction between logs as they move in a rotating cylindrical drum. the barks carried away in a stream of water, strained out and burned

Hydraulic Debarking-a jet of high P water is directed tangetially to the bark and strips away the bark cleanly, breaks it and is sluiced away. Recovered bark is compressed before burning and facilitate combustion.

PULPING PROCESS Goal: to release the fibrous cellulose from

its surrounding lignin but keeping them intact (more useful fibers)

obtai good color w/o degradation and loss of yield

Kraft Process Also known as sulfate pulping Main additive: Na2SO4 Na2S NaOH Na2CO3

Step by Step Process Logs are cut to convenient lengths and

debarked

Chippers large rotatong disk holding 4 or more heavy knives

Screening - separate oversized chips, the desired prod, and sawdust, OS resent to chipper

Presteaming in the digester --- volatilizing the turpentine and non condensable gases

Step by Step Process meets cooking liquor 1.5 hrs at 170C quick quench flow of cold cooking liquors

stops cooking countercurrent displacement washing to

reduce chemical content of chips followed by pulp contcentration (dewatering) chips with adhering liquor known as brown

stock used liquor ---> black liquor recovery process

BLEACHING bleaching agents (reducing agent)Na2S2O4, sodium borohydride or bisulfite

oxidative bleachesO3, Na2O2, H2O2,ClO2, Cl2

chlorine and hypochlorite -- oxidize and destroy the dyes and tannins of the wood and leave chloride residues in the wash water and harm the cellulose fibers. chlorine dioxide was found better

Pulp is then diluted -- uses much water contaminating all of it

Recovery of Black Liquor contains 95 to 98 pct of the chemicals charged to

the digester

organic sulfur compounds, traces of lime, iron oxide , alumina, and potash

Thomlinson kraft recovery furnace , black liquor conc to 35% solids, multiple effect evaporator

sprayed to thomlinson furnace where it is burned from sulfate to sulfide, steam and molten salt mixture or smelt --- combustible

SULFITE PULPING HIGH QUALITY LOW QUANTITY

high energy requirements

digestion of wood in aqueous solutions of calcium bisulfite and SO2

sulfonation and solubilization of lignin and hydrolytic splitting of lignin complex

Step by Step Process oxidation of S to SO2 cooled in a horizontal cooler gas absorption in the presence of Ca, Mg,

or NH4 compounds (absorption tower) liquor charged to digesters 4.5 % SO2 3.5

% of which are free direct steam injection for heating HE minimizes dilution of liquor

Step by Step Process After the cooking process, blown to a tank

equipped w/ means to wash pulp with fresh water red liquor is burnt in a boiler to produce steam

where MgO and SO2 are formed and returned to acid tower

Screening Centrifugation to remove foreign matter Bleaching, bleaching is easy but fibers are weak.

replaced by kraft process when ClO2 bleaching made it practical

Milk of lime to neutralize the mass Washed and thickened

Semichemical or NSSC pulping neutral sulfite semi-chemical (NSSC)

high yield but poor quality and bleachability

milder cook

Thermomechanical Pulping no chemical treatment high T soften the lignin and make fibers

less difficult to separate fibers are coated with lignin best for

fiberboards chemical decomposition of non-cellulosic

constituents and results in pulp brittleness and discoloration

Paper Processing Pulp --->> Paper

lacks desirable properties in a finished paper

Opacity

Strength

surface feel

Beating Hollander beater

wooden or metal tank having rounded edges and a partition way down the middle on one side is a roll equipped with knives directly below a bedplate consisting of stationary bars

beating the fiber makes the paper stronger, more uniform, denser , more opaque and less porous

Paper Additives Filler and Dyes added to the mixture and beaten to

uniformity.

Fillers are finely ground organic material that improves the brilliance, whiteness, printability, and opacity of the material. e.g. talc, clay, silicoaluminates, CaCO3, TiO2

Sizing agent is added to paper to improve resistance to penetration by fluids. most common sizing agent: rosin soap from tall oil or wax emulsions

Improves the ability to take ink well and resist erasures

Types of Paper Processing Cylinder Machine -for heavy paper and

cardboard, utilizes 4 to 7 vats where stocks are charged

Fourdrinier machine

Fourdrinier Machine dilute stocks from prev operations is sent

through screens (50% fiber) fiber remains on the screen while water runs

through screen shakes to give better fiber orientation

Rubber deckle straps along the sides of the screens to form the paper's edges

Pass through a series of press rolls Drying rolls heated internally by steam (60-

70pct to 90-94pct) Sizing, final surfacing