Post on 20-Jul-2016
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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