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Pulp and Paper Making in South Africa

Pulp and Paper Making in South Africa. Raw Materials Derived from Renewable Resources . Pulping Processes. 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.

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Pulp and Paper Making in South Africa

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  1. Pulp and Paper Makingin South Africa

  2. Raw Materials Derived from Renewable Resources

  3. Pulping Processes • Chemical Pulping • Mechanical Pulping • Chemo-Mechanical or Semi Chemical • Waste Repulping

  4. 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.

  5. 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

  6. 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

  7. 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

  8. Chemi-thermomechanicalPulps (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)

  9. Chemical Pulping Chemicals degrade & dissolve the lignin. 􀂾 Hemicellulose also removed. 􀂾 Mainly secondary wall material remains

  10. 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

  11. 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

  12. 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

  13. 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 %)

  14. Beating andRefining 􀂾 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

  15. Beating andRefining 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

  16. Chemical vs. Mechanical Pulping

  17. Chemical vs. Mechanical Pulping

  18. Bleaching ProcessesConventional • 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

  19. Bleaching ProcessesModern Trends • Sulpher Dioxide • Oxygen (radical mechanism) or Ozone (addition over the C=C) • Chlorine Dioxide • Alkali Extraction • Chlorine Dioxide • Hydrogen Peroxide • Exotics

  20. Paper Making Chemicals • 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

  21. Major Grades of Paper

  22. 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

  23. Per Capita Paper Consumption kg

  24. Pulp and Paper Makingin South Africa

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