Pulp Mill



2A) Chemical Bagasse Pulp Mill

  • 2A.1 ) Cooking .
     The depithed , washed and cleaned bagasse is conveyed to the digester house to be cooked by means of caustic soda in a continuous Pandia digester and heated by steam under high pressure , thus allowing the caustic soda to permeate the bagasse and dissolve all non – cellulosic substances and producing unbleached pulp .

  • 2A.2 ) Washing and Screening .
    Washing of brown stock is done in a three stage drum washing system and screening system is installed between second and third drum washer which consists of two pressure separation screens, one vibration screen and a sand separation unit. After the washer the pulp is pumped via Hi –Shear mixer to the bottom of the oxygen reactor .

  • 2A.3) Oxygen Delignification .
    In the Hi- Shear mixer the pulp is mixed with caustic soda and oxygen gases after being heated up tp 95oC before the mixer .

    In the oxygen reactor the pulp is performed to delignification with oxygen .The pulp is then washed in three consecutive wash filters. The main task of the third oxygen wash filter is to reduce the organic carry – over to the final bleaching as much as possible to limit the formation of chloroganic compounds in the Do-Stage .

  • 2A.4) Bleaching.
    Bleaching is done in a three stage sequence, D0-E0-D1.The washed and dewatered pulp from the third oxygen wash filter is conveyed through a Hi-shear mixer where CLO2 water is added, to the D0 tower from which it is discharged to the D0-washer .

    After the addition of NaOH and through a steam mixer , a MC - pump after adding the oxygen transfers the pulp to the injection ring and to E0-tower , then to the E0 washer .The pulp is then dropped to the stand pipe of the MC-Pump for the D1-tower and is pumped through a Hi-shear mixer where CLO2 is added ,to the final D1-tower .

    Final washing is performed again on a vacuum drum washer before storing the bleached pulp in the MD storage towers.

2B ) Chemi - Thermo Mechanical Pulp (CTMP )Mill .

  • 2B.1) Bagasse Receiving System .
     The system starts with a storage silo for collecting accept fibers from the wet cleaning lines.

    The plug screw feeder of the pressurized heating screw is fed evenly with bagasse via a pin drum feeder while the excess is returned to the bagasse storage bin .

    The plug screw feeder forms a pressure tight plug of bagasse and a blow back valve is situated opposite the plug screw feeder to prevent blow back of steam.

  • 2B.2) Chemi – Thermo Mechanical Pulping System .
    After bagasse is dewatered and compressed in the plug feeder, sodium sulfite and caustic are applied and bagasse expands and absorbs the liquor.

    A pressurized heating screw follows after which bagasse is fed to the primary pressurized single disc refiner .The pulp is then blown to an intermediate chest.

    After a certain retention time and through a dewatering screw press, pulp is conveyed to a secondary atmospheric single disc refiner after which it is fed to screening and cleaning system .

  • 2.B.3) Screening And Cleaning System
    Screening is effected by two primary pressure screens in series and one secondary pressure screen.

    The accepts from the second primary screen are conducted to a twin wire press and the rejects of primary screens are rescreened in the secondary pressure screen.

    A centri – cleaner system is utilized for sand removal

  • 2B.4 ) Dewatering , Bleaching and Storage System :
    On the twin wire press the stock is dewatered from 3 % consistency to 35 % and then fed by gravity into a screw conveyor feeding a high consistency mixer where the bleaching liquor (H2O2) is added .The stock is then blown directly into the bleaching tower, from where it is rediluted and pumped to a twin wire wash press. This provides proper washing of the pulp before it is further processed in the hydrosulfite bleaching stage after which it is transferred to a storage tower feeding the paper mill for newsprint production.