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Pulps are subjected to a wide range of procesing steps, depending on their method of preparation (mechanical, semichemical, chemical virgin pulp, secondary fiber) and their use.1. DeFiberingAll high-yield chemical and semichemical pupls must be defiberized by mechanical means following the cooking steps. Defiberization of chemical pulps should be considered apart from pulp refining which is carried out in the paper mill; however, it must be reconized thet the method and degree of defiberization will have an effect on later refining requirements.2. Deknotting This case explain that knots are removed from the pulp prior to washing, and are either discarded as waste or return to the digester infeed. Two types of knotters are in use. The olders vibrating screen knotters do an efficient job of knot separation, but the open type design generated foam and liquor spatter, and need operator attention.3. Brown Stock washing and Screening The cooked pulp from digester must be washed, with the objective to removed residual liquor and recover the maximum amount of spent chemical with minimum dilution. Alternative methods are available to challenge the predominant position of the Rotary vacuum Washer of which the element of a vacuum washer is a clothcovered cylinder that rotates in a vat containing the pulp slurry. Difussion wshing was first applied to the chip mass in the bottom of the Kamyr continius digester. The Kamyr Pressure diffusion washer is similiar in operation to the Kamyr sawdust digester internal washer, and was design principally for placement in series with the kamyr digester internal washer.The pulp at blow line consistency is intr6duce at the top of the vessel and is caused to flow downward throught an annulus formed by a slighly tapered silindicar screen and a central liquor chamber. Press washer show the pulp mat is formed on the surface of the cilynder and the waterd with the aid of pressure applied inside the water hood as opposite to vacuum inside the cilynder.The horizontal Belt washer resembles the fourdriner section of the paper machine. The pulp suspentionis distributed from a headbox onto a travelling filter belt and formed into a mat. Dilution/ Extraction equipment is the oldest method of pulpng washing. The efficiency of type the system is dependent upon the ratio of the discharge to the incoming consistency and the amount of dilution water added to the system. The Norden’s Method efficiency factors is defined as the number of mixing stage which give the same result as washing equipment under considering when operated at the same wash liquor ratio.Screening is required to remove oversized, troublesome, and anwanted particles from good papermaking fibers. The major type of screening is vibration, gravity sentrifugal and pressure.
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