With the help of flow sheet, explain the manufacturing process of paper by Kraft process.

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written 7.2 years ago by

akshayshevate09 • 0

The Kraft process of pulp making uses sodium sulphate, sodium hydroxide and sodium sulphide as the digester chemicals.
1. The spent liquor produced is known as Black liquor. The black liquor is treated seperately for the recovery of chemicals.
2. The cellulosic fibre after being seperated from the black liquor is washed and then partially dewatered in a cylindrical screen called Decker.
3. A concentrated wash water may be sent for chemical recovery, the dilute wash water forms the waste water. This volume of waste water is known as Brown Stock wash or Unbleached Decker watste.
4. The washed cellulosic fibres are then sent for the bleaching in three stages where chlorine, caustic and hypochlorite are used in successive stages.
5. Waste water from first and last stages are light yellow in colour while that from the caustic extraction stage is highly coloured.
6. The bleached pulp is then sent for the paper mill.
7. In paper mill, the pulp is disintegrated and mixed with various filler materials like alum, talc and dyes in an oblong shaped specifically made tank known as Beater. After beating, the pulp is redefined in a machine known as Jordan.
8. The pulp is carried by a travelling belt of fine screen to a series of Rolls where the final product the paper is produced.
9. The drained water often called as White Water forms the waste water from the paper mill section, this waste water contains fine fibres, alum, talc etc.
10. The black liquor of the Kraft process is concentrated by evaporation and then incinerated with the addition of sodium sulphate.
11. The organics like lignin, resin etc are burnt out and the smelt is dissolved in water. The resulting liquid is known as Green Liquor.
12. Lime is now added to this liquor resulting in formation of White liquor and Lime mud.
13. Some very toxic waste material are also generated during the process of chemical recovery from black liquor like Dimethyle Sulphide, Methyl Mercaptan etc.

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