Transcript Pulp and Paper Making in South Africa

Pulp and Paper Making
in South Africa
Raw Materials
Derived from Renewable Resources
Pulping Processes
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Chemical Pulping
Mechanical Pulping
Chemo-Mechanical or Semi Chemical
Waste Repulping
Mechanical Pulping
Mechanical action breaks the ML which is more
brittle than the fibre wall.
• The fibre wall is left intact, but substantial fibre cutting occurs
• Chemical composition is not altered very much.
Mechanical Pulping
Wood physically taken apart –
recovery high
• Dense species not usually used
due to short thick walled fibres
and high % of vessels
•Resinous species can also
present problems
•Yield - high but pulp unsuitable for many uses due to lignin
content which stiffens fibres
• Lignin also results in yellowing of pulp with time
Mechanical Pulping -SWG
Mechanical Pulping – SWG
Pulp produced by pressing logs
against rotating grindstone
􀂾 Fibres are compressed, and
loosened
􀂾 Friction creates heat to soften
the lignin
Mechanical Pulping -Refiner
Mechanical Pulp (RMP)
Wood chips are broken down into fibres by bars on
two rotating or one rotating and one stationary discs
Chemi-thermomechanical
Pulps (CTMP)
To decrease energy cost or to improve pulp quality,
chemical treatments (alkaline sulphite, sodium
sulphite) are often added to mechanical pulping
􀂾Pretreatment of chips (to lower energy)
􀂾Inter-stage treatment (lower energy, increase fibre
flexiblity)
􀂾Post-treatment (fibre flexiblity)
Chemical Pulping
Chemicals degrade & dissolve the lignin.
􀂾 Hemicellulose also removed.
􀂾 Mainly secondary wall material remains
Chemical Pulping
• Soda
• Soda Anthra Quinone
• Kraft = Caustic Soda + Sodium Sulphide (High
strength; efficient recovery of chemicals; handles a
variety of species; tolerates bark)
• Neutral Sulphite Semi Chemical = Sodium
Carbonate + Sodium Sulphite
• Sulphite – H2SO3 + bisulfite; bright pulp & easy to
bleach; higher yield; easier to refine
Kraft Recovery Cycle
• Black Liquor is Concentrated in Multiple Effect
Evaporators to about 65 – 70% Solids
• This Heavy Black Liquor is fired in a Soda
Recovery Furnace
• The Smelt is dissolved in water to form Green
Liquor – Sodium Carbonate and Sodium Suphide
• Green Liquor is causticised with un-slaked lime,
filtered and polished to form white liquor
• The Calcium Carbonate sludge is burnt in Kilns
Soda Recovery
• Soda or Soda/AQ Liquor is concentrated to 55-60%
Solids in Multiple Effect Evaporators
• Strong Liquor is sprayed to form droplets in a
Fluidized Bed Reactor
• Further evaporation takes place as droplets fall
• Organics burn in the fluidized bed
• Inorganics recovered in the form of Sodium
Carbonate
Washing
􀂾 Aim is to:
• minimize black liquor carryover
• recover dissolved solids
􀂾 Solution contains
• Lignin (30-45 %)
• Hemicellulose (28-36 %)
• Extractives (2-5 %)
• Na2O (25-40 %)
Beating and
Refining
􀂾 Purpose
􀂾 To flatten fibres to ensure maximum surface area
for hydrogen bonding in paper
􀂾 Beating also unravels fibres
􀂾 Beating is done in refiners
􀂾 Fluted plug rotates inside
similar shaped housing with ribs
Beating and
Refining
Freeness
􀂾 Freeness is term used to
describe pulp potential
􀂾 Measured by rate of water passing through set
amount of fibre formed on wire mesh
􀂾 Well beaten fibre does not allow water to
pass, so Freeness is low
􀂾 Burst and tensile strength increased by
beating time – increases inter-fibre bonding
Chemical vs. Mechanical Pulping
Chemical vs. Mechanical Pulping
Bleaching Processes
Conventional
• Chlorination – Elemental Chlorine (aromatic
substitution of H and addition reactions over the
C=C)
• Alkali Extraction – Sodium Hydroxide
• Chlorine Dioxide or Sodium Hypochlorite
• Alkali Extraction
Bleaching Processes
Modern Trends
• Sulpher Dioxide
• Oxygen (radical mechanism) or Ozone (addition
over the C=C)
• Chlorine Dioxide
• Alkali Extraction
• Chlorine Dioxide
• Hydrogen Peroxide
• Exotics
Paper Making Chemicals
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Cellulose Fibers – the bulk
Fillers – Clay, Calcium Carbonate – 0 to 25%
Strength Additives – Starch, CMC – 0 to 10%
Sizing Agents – Rosin + Alum, AKD, ASA
Wet Strength Additives – 0 to 2%
Dyes
Retention Agents
Major Grades of Paper
South African
Pulp and paper Industry
• Number of Paper & Board Mills – 17
• Number of Pulp Mills – 9
• Paper & Board Capacity = 2.421 Mt –
Local Consumption = 75%
• Pulp Capacity = 2.472 Mt –
Local consumption = 60%
• The Industry is a very important foreign exchange
earner
Per Capita
Paper Consumption kg
350
300
250
1993
1999
2002
2004
200
150
100
50
0
USA
Europe
RSA
WORLD AFRICA
Pulp and Paper Making
in South Africa