Pulp & Paper Exam 2

CHEN 5090 Exam 2

knot

Fraction of pulp that is retained on a 3/8” perforated plate

defibering

Improves the fiber properties and reduces the refining requirements later

brown stock washers

The most removal of pulping chemicals and lignin with the least amount of wash water

cleanliness of the pulp and the amount of water used

compromise of brown stock washing

pulp moves opposite direction of the wash water

brown stock washing sequence

washing and leaching

brown stock washing mechanisms

leaching

diffusion and desorption

diffusion

dissolved solids and chemicals in the interior of the pulp fibers must move into the surrounding liquor to be removed

desorption

attached dissolved solids and chemicals leaved the fibre surface for the surrounding liquor

displacement

liquor in the pulp is displaced with weaker wash liquor or clean water

dilution/extraction

pulp slurry is diluted and mixed with weak was liquor or clean water. then the liquor is extracted by thickening the pulp.

rotary vacuum washer

type of washer used at IP

drop leg

applied to siphon the water from the washer

specific loading

oven dry tons of pulp per square foot of cylinder surface

air

as much as possible must be removed to avoid foaming problems

dilution factor

weight of wash water introduced into the black liquor per unit of weight of oven dry pulp being washed

displacement ratio

measures the effectiveness of a single washing stage

displacement ratio

=(Cv-Cs)/(Cv-Cw)

thickening factor

(Win-Wout)/Win

wash loss

amount of washable compounds in the pulp suspension that could have been removed in washing

soda loss

washable sodium content of the pulp leaving with the pulp

total soda loss

washable sodium and chemically bound sodium leaving with the pulp

drum displacer

incorporates all washing stages on a single rotary drum

horizontal belt washer

resembles fourdrinier

diffusion washing

submerged environment, long contact time between the chips and the washing water

kamyr atmospheric diffusion washer

kamyr used at IP

brown stock washing efficiency

determined by the amount of solute is removed and the amount of wash water needed to remove that solute

norden’s method

measures the degree of polymerization (viscosity test)

screening

operation of removing oversized, troublesome particles and shives

vibratory

type of screen, obsolete, rotary of flat form

gravity centrifugal screens

type of screen, mostly obsolete, good fibers hydrate well and align themselves with the direction of the flow, while coarse fibers do not hydrate well and are carried across the plate

pressure

type of screen that is most dominantly used, utilizes perforated cylindrical plates

Er

=(Sr/Si)\*Rw

centrifugal cleaning

removal of contaminants or unwanted particles from pulp and paper stock by centrifugal force and fluid shear

3\.5-4%

slusher, pulp is retained on the cylinder and excess water passes through wire mesh cylinder

4-8%

gravity thickener, same as slusher but a couch roll is added

10-12%

valveless washers are used

dilute stocks to 12%

multidisk thickeners are used

12-16%

vacuum washers are used to extract more water from the pulp slurry

above 15%

screw presses are used

newtonian fluid

has constant viscosity regardless of the shear rate or applied stress

blending

reduces variations in kappa number and improves the bleaching control

dewatering

needed if transporting pulp

boiling point rise

liquid mixture that contains dissolved organic and/or inorganic substances will boil at a higher temperature than water at the same pressure

sodium sulfite

compound that sulfur is converted to during chemical recovery

13-18%

concentration of solids in black liquor leaving the washers

60-80%

what is the ideal solid concentration in black liquor before burning in the recovery furnace?

steam is applied countercurrent to the liquor

how do multi-stage evaporators work?

long tube

most common type of evaporator unit, entering weak liquor boils and thickens as it travels quickly up the tubes

thermosiphon

fluid, usually a liquid or a gas, is driven by temperature differences. It is a passive system that does not require any mechanical pump or external power source to move the fluid

falling film

indirectly heated evaporators, industry standard

cascade

type of evaporator that consists of a series of steel tubes arranged cylindrically in a rotating wheel immersed in black liquor

cyclone

type of evaporator where liquor is sprayed into the gas as it enters

venturi evaporator-scrubber

type of evaporator where the black \n liquor is sprayed into a turbulent flow of \n the flue gas as it passes through a \n venturi throat.

black liquor oxidation

required only if direct contact evaporators are in operation

oxidation

converts unstable sulfide to a stable thiosulfate

concentrator

indirectly heated evaporators, most common type is falling film with recirculation

evaporates water, burns organic matter, supplies heat to make steam

3 functions of a recovery boiler

drying, oxidation, reduction

zones of the recovery boiler furnace

function of caustic plant

convert Na2CO3 to NaOH\`

green liquor clarifier

removes insolubles, unburned carbon, and inorganic impurities

slaker

mixes with violent agitation of green liquor with CaO at elevated temperatures

calcining

converts lime mud back to CaO for reuse

calcining

lime kilns are used for

drying, heating, maintaining

3 phases in calcining

repulping

mechanical action to disperse dry, compacted pulp fibers into pulp slurry

refining

to develop and modify the structure of pulp fibers to optimize the properties of the paper product

refining

strains fibers by the transfer of energy from the beating element to the fibers

bruising

refining at higher consistencies with a large gap between the refiner plates creates this. increases paper strength and density

cutting

refining at low consistencies with a small distance between refiner plates creates this. increases quality of formation

refining

fibers move parallel to the bar crossing

beating

fibers move perpendicular to the rotating bars

refining

does refining or beating have better control, lower operating costs, and is quicker?

facilitate sheet making

an objective for beating/refining

high

level of consistency that produces curled, kinky fibers with low bonding ability after refining

medium

level of consistency that produces curled, microcompressions, internal fibrillation, and swelling

refining

optimize strength development and control of stock drainability and sheet formation

fiber flexibility

important because it controls the development of fiber to fiber contact during drying

blend chest

where pulp stock and additives are mixed with an agitator

machine chest

contains the final furnish mixture