Kraft process

1. KRAFT PROCESS

2. T he kraft process  also known as kraft pulping or sulfate process Is an industrial process for conversion of wood into wood pulp consisting of almost pure cellulose  fibers Treatment of wood chips with a mixture of sodium hydroxide and sodium sulfide, known as liquor , That breaks the bonds that link lignin to the cellulose

3. Pulping The problem Wood (this is what we have) Fibers (this is what we want)

4. History German word  Kraft meaning paper invented by  Carl F. Dahl in 1879 a pulp mill using this technology started in   Sweden in 1890. The invention of the  recovery boiler  by  G.H. Tomlinson   in 1930s. 

5. Kraft Pulp Making Process

6. RAW MATERIAL

7. Impregnation Cooking Recovery process Blowing Screening Washing Bleaching Process chemicals STEPS INVOLVED IN PROCESS

8. IMPREGNATION Common wood chips used a re 12–25 millimeters long Prestreamed and wetted to impregnate the chips with white liquor White liqour contain NaOH+NaSH

9. COOKING enters the digester below 100 °C (212 °F). Typically delignification requires several hours at 170 to 176 °C (338 to 349 °F). The combined liquids, known as black liquor contain lignin fragments, carbohydrates from the breakdown of hemicellulose,  sodium carbonate ,  sodium sulfate  and other inorganic salts.

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11. Thermochemical sulfate reduction 1. Na 2 SO 4  + 2 C → Na 2 S + 2 CO 2   Calcium carbonate  precipitates from white liquor 2. Na 2 S + Na 2 CO 3  + Ca (OH) 2  ←→ Na 2 S + 2 NaOH + CaCO 3 Calcination 3 . CaCO 3  → CaO + CO 2 Slaking 4. CaO + H 2 O → Ca (OH) 2 RECOVERY PROCESS

12. Blowing Screening Washing Screening of the pulp after pulping is a process whereby the pulp is separated from large shives, knots, dirt and other debris Pressure diffusers Atmospheric diffusers Vacuum drum washers Drum displacers Wash presses cooked wood chips are blown by reducing the pressure to atmospheric by release of steam

13. In bleaching tower the pulp are bleached to a high brightness Bleaching

14. Process chemicals Process chemicals are added to improve the production process : Surfactants  may be used to improve impregnation Anthraquinone  is used as a digester An  emulsion breaker  can be added in the soap separation Defoamers  remove foam Dispersing agents ,  detackifiers  and  complexing agents  are keeping the system cleaner Fixation agents  are fixating finely  dispersed  potential deposits to the fibers