Exam Revision

Question 1

What are the most common raw materials?

Answer 1

Mechanical pulp, chemical pulp, and recovered paper and board grades.

Question 2

Name examples of chemical pulps

Answer 2

Softwood, hardwood, Kraft, Sulphite

Question 3

Name examples of mechanical pulps

Answer 3

SGW, PGW, TMP

Question 4

What are specifications for pipe guiding?

Answer 4

• distances have to be as short as possible
• as few bends and kinks as possible
• no dips

Question 5

What are the specifications for pipe connections?

Answer 5

• no 90 degree connections
• always inject side stream into main stream
• consider flow dynamics

Question 6

What are the 4 main purposes of disintegrating and slushing?

Answer 6

• disintegration/de-fibering
• ink detachment
• mixing/homogenisation
• contaminant removal

Question 7

What are the 3 main pulping groups and their consistencies?

Answer 7

• LC pulping (<7%)
• HC pulping (15-25%)
• drum pulping (>18%)

Question 8

How does pulping (disintegration) occur both mechanically and chemically?

Answer 8

Mechanically: separation of fibres and contaminants and flake reduction via shear forces and turbulence.
Chemically: fibre swelling and viscosity reduction via heat and additives.

Question 9

How does pulping (ink detachment) occur both mechanically and chemically?

Answer 9

Mechanically: gently rubbing off the ink particles from the fibre surface by shear forces and fibre-to-fibre friction.
Chemically: viscosity reduction, fibre swelling, chelation and influencing fibre polarity through heat and additives.

Question 10

How does pulping (contaminant removal) occur moth chemically and mechanically?

Answer 10

Mechanically: physical separation of contaminants from fibres to protect machinery, via raggers, detrashing units, junk traps and screen plates.
Chemically: N/A

Question 11

How does pulping (mixing/homogenisation) occur both mechanically and chemically?

Answer 11

Mechanically: to provide a homogeneous suspension via turbulence.
Chemically: viscosity reduction via heat.

Question 12

What are the main pump specifications?

Answer 12

• capacity
• head
• degree of stock contamination
• stock consistency
• gas content
• pulsations

Question 13

What are the four most common types of pumps?

Answer 13

• single suction pumps with open impeller
• single auction pumps with closed impeller
• single suction mid consistency pumps with screw impeller
• double suction pumps with closed impeller

Question 14

What are ‘single suction pumps with open impellers’ mainly used for?

Answer 14

Suitable for most applications but commonly used for suspensions up to 6%

Question 15

What are ‘single suction pumps with closed impellers’ used for?

Answer 15

Mainly for pumping process water

Question 16

What are ‘single suction MC pumps with screw press’ used for?

Answer 16

Used for pumping MC stock after dewatering or bleaching stages

Question 17

What are ‘double suction pumps with closed impeller’ used for?

Answer 17

Mainly in approach flow due to high capacity and low pulsation

Question 18

What is the main purpose of HC cleaning?

Answer 18

To remove heavy and abrasive contaminants from damaging machinery further in the process. These contaminants are: glass, metal, sand.

Question 19

Where in the process would you find HC cleaners?

Answer 19

After pulping but before screening and cleaning.

Question 20

What is the consistency and differential pressure required for HC cleaners?

Answer 20

Consistency = 3-6%
Differential pressure = 0.8-1.5 bar

Question 21

What is the purpose of coarse screening?

Answer 21

The removal of coarse contaminants and residual flakes

Question 22

What consistency is required for coarse screening?

Answer 22

2-5%

Question 23

What machinery is used for coarse screening?

Answer 23

Screen plates or baskets with holes

Question 24

What is the purpose of fractionation?

Answer 24

Separation of long and short fibre fractions.

Question 25

What consistency is used for fractionation?

Answer 25

0.2-2%

Question 26

What machinery is used for fractionation?

Answer 26

Slotted screen baskets with a low profile angle.

Question 27

What is the purpose of fine screening?

Answer 27

The removal of fine contaminants and stickies.

Question 28

What machinery is used for fine screening?

Answer 28

Slotted screen baskets

Question 29

What consistency is used for fine screening?

Answer 29

0.8 to 2%

Question 30

What are key parameters for screens?

Answer 30

- screen area - hole diameter or slot width - Open screen area - screening element profile - Rotor type / speed/ clearance

Question 31

What is removed during low consistency cleaning?

Answer 31

Light particles and stickies.

Question 32

Why is a low consistency used during low consistency cleaning?

Answer 32

To reduce collisions with fibres and increase separation efficiency of small particles.

Question 33

How many stages of cleaners do you typically find in low consistency cleaning?

Answer 33

4 to 6

Question 34

What is a forward cleaner?

Answer 34

A heavy reject cleaner while rejects are collected at the bottom

Question 35

What is a reverse cleaner?

Answer 35

A light reject cleaner where rejects are collected at the top.

Question 36

What is a Combi cleaner?

Answer 36

A heavy and light reject cleaner with heavy rejects collected at the bottom and light reject collected at the top near the accept flow.

Question 37

What are the four main purposes of floatation deinking?

Answer 37

- ink removal - Sticky removal - ash removal - brightness increase

Question 38

How does deinking work?

Answer 38

Deinking chemicals are added which allows hydrophobic substances to detach from the fibre surface and are consequently floated via air bubbles to the stock suspension surface.

Question 39

What is a suitable consistency for floatation deinking?

Answer 39

0.8 to 1.2%

Question 40

What is the purpose of deinking soap?

Answer 40

To increase surface activity and to collect ink stickies

Question 41

What is the purpose of caustic soda in deinking?

Answer 41

To cause fibre swelling, saponification of fatty acids, ink binder emulsification.

Question 42

What is the purpose of hydrogen peroxide in deinking?

Answer 42

As a bleaching agent to counteract the yellowing caused by caustic soda?

Question 43

What is the purpose of sodium silicate in deinking?

Answer 43

Ink dissolution support, HOO- stabiliser

Question 44

Why is calcium chloride sometimes used in deinking?

Answer 44

To ensure a water hardness of 5° dH

Question 45

What is the purpose of thickening?

Answer 45

- Water removal - Separation of solids from water

Question 46

What generally is the consistency in and out of a thickener?

Answer 46

In = 0.5% - 2% Out = 4.5% - 15%

Question 47

What machinery is typically used in thickening?

Answer 47

- disc filters/thickeners - drum thickeners

Question 48

What is the purpose of dewatering?

Answer 48

- water removal - separation of solids from water

Question 49

What are the general consistencies in and out of dewatering?

Answer 49

In = 3.5% - 15% Out = 25% - 40%

Question 50

What machinery is typically used for dewatering?

Answer 50

- screw press - wire press

Question 51

What is the purpose of washing?

Answer 51

To remove substances (e.g. ash) from fibres

Question 52

What are the general consistencies in and out of washing?

Answer 52

In = 0.7% - 1.3% Out = 7% - 10%

Question 53

What machinery is typically used during washing?

Answer 53

- belt washer

Question 54

What is the general purpose of a disc filter?

Answer 54

- to thicken the stock suspension - to provide dilution water (cloudy, clear, super clear filtrate) - to separate water loops

Question 55

How is the required pressure for filtration maintained during filtration in a disc filter?

Answer 55

By the geodetic height (head) of filtrate water columns.

Question 56

What is the purpose of deflaking? How does this occur?

Answer 56

Deflaking is done to: - disintegrate fibre bundles - disintegrate wet-strength paper components - disintegrate coated broke Heavy acceleration in changing directions cause heavy impacts, breaking up flakes.

Question 57

What are the features of deflakers? Where are they positioned in the process?

Answer 57

- toothed fillings - intensive acceleration and retardation - no refining effect - low specific energy consumption compared to pulping Positioned after pulping, but before refining, within the fine screening plant.

Question 58

What is the purpose of disperging? How does this occur?

Answer 58

The purpose of disperging is - destroying and dispersing dirt specs - destroying and dispersing dirt stickies This dispersion occurs via high shear impact forces at high temperatures

Question 59

Where in the process would you find disperging?

Answer 59

- after the disc filter and thickening - thickening -> heating -> disperging

Question 60

What is the definition of a water loop?

Answer 60

The total of all water flows in a process chain where the first step is a dilution process, and the final step is a thickening process.

Question 61

What are the advantages of a partially or fully closed water loop?

Answer 61

- reduced fresh water consumption - low fresh water treatment costs - lower waste water (and therefore discharge costs) - higher temperatures in the approach flow (and therefore better dewatering) - enables paper production in arid regions

Question 62

What are the disadvantages of partially or fully closed water loops?

Answer 62

- high concentrations of contaminants in the water loops - increased biological activity (acidification, slime) - problems with retention, runtime efficiency and deposits - need for cooling - loss of strength