Pulp & Paper Quiz 2

extracitives

provides fungal & insect resistance, 7% SW, 4% HW, contains ash content, consumes bleaching chemicals & increases pitch —> detrimental in pulp

increasing fiber length causes (on sheet impact)

increases tear, increases tensile, decreases formation

increases CWT (cell wall thickness) causes (on sheet impact)

fiber gets stiffer, poorer bonding, decreases tensile, increases tear, increases formation

fiber length of SW & fiber length of HW

SW = 3.5-7.0 mm
HW = 1.0-1.6 mm

sheet properties of boxes

high tensile strength & high tear resistance

debark

ensuring feedstock is free of bark and dirt, removes concentration of dead cells, minerals, nails, barbed wire, etc.

chipping

used to control the thickness of chips

kraft pulping

type of chemical pulping that is used to eliminate lignin, dissolving wood chips into pulp, good pulp strength, low energy requirements and chemical cost, low yield

ideal chip size

20 × 30 × 2 mm

chip size impact on pulping & bleaching

reject chips

dust/fines can be burned for fuel

lonogs/oversized can be rechipped

knots can be made smaller

knots

darker because higher lignin concentration, difficult to get chemicals inside, produced when a side branch is broken off

mechanical pulping

causes damaged fibers (short & stiff) & poor bonding, lignin is unremoved, more energy input required, higher yield (96%), scatters light well, used for newspaper or paper requiring little strength

chemical pulping

long fibers & high bonding, less energy input required, less yield (45%), dissolve the lignin wile preserving teh carbohydrates, used for high quality papers

groundwood

type of mechanical pulping produced by grinding wood

thermal mechanical pulping (TMP)

uses steam & mechanical force to break wood chips into papermaking

light scattering

increased by the number of debris, mechanical pulp contains more debris

pH of kraft pulp
pH of neutral sulfite semi chemical (NSSC)

kraft pulp = 13+ (high)

NSSC = 7-9 (neutral)

freeness test

determines how freely plup gives up H2O —> measure of consistency
mechanical pulps are less free —> drain very slowly as fragments hold onto H2O

canadian standard freeness (CSF)

provides correct temp. based on freeness test
higher # = higher freeness because higher overflow, faster draining

lower # = slower draining

batch digester

filled with chips, white liquor & black liquor, fentirely and closed, let cook, open and blow out, repeat cycle

longer cycle time

allows you to sequence your downs (keeps mills running during maintenance), allows you to swing between HWs and SWs

continuous digester

more compact size, faster cycle time (as loading and blowing operations are not required), steady energy demand

white liquor

cooking liquor, fresh pulping liquor for the kraft process containing NaOH, Na2S, variety of impurities, 2% will be made, 97-98% will be recovery

black liquor

waste liquor, contains original inorganic components & high concentration of dissolved organics (lignin, fragments of glucose), 13 pH

green liquor

partially recovered kraft liquor (intermediate liquor in recovery sequence), molten smelt, contains Na2CO3 & Na2S

active alkali (AA)

total of NaOH + Na2S

effective alkali (EA)

total of NaOH + ½ Na2S

activity

ratio of AA to total titratablel alkali (TTA)

sulfidity

ratio of Na2S to AA

5 zones of chemical pulping

1. impregnation 2. heating. 3. cooking 4. wash 5. cooling

kinetics of kraft pulping

ion transfer into the chip by penetration & diffusion, adsorption of the ions on the surface of the wood constituents —> reactions between wood constituents & adsorbed ions, desorption of the reaction products (liquid form, dissolved solids), transport of the reaction products to the exterior of the chip

steaming

efficient removal of air, diffusion into the capillaries, condensing & evaporating again to complete the air displacement

penetration

complete and uniform penetration by the cooking liquor, sufficient reagent concentration, capillary forces and pressure which must be overcome, occurs through vessels in HWs and lumina via pits in SWs

diffusion

controlled by the temperature, easy transport longitudinally (3-4x more open than in radial or tangential direction), harder transport tangentially & through the growth ring, occurs whenever water is present, effective across grain, affected by wood density

Na2O basis

indicates actual chemical relationship between chemicals in a kraft cook