Liquid purification or separation – Filter – With residue removing means or agitation of liquid
Patent
1998-04-07
1999-07-20
Lithgow, Thomas M.
Liquid purification or separation
Filter
With residue removing means or agitation of liquid
210414, 210304, 210308, 162 55, 162251, 209 17, 209273, 209250, 209306, B07B 120, D21D 502, D21D 516
Patent
active
059252499
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an arrangement for screening pulp suspensions in order to separate impurities and other pulp fractions, which are not desired to be included in the final product, such as coarse particles, undefibered material and poorly worked fibers.
BACKGROUND OF THE INVENTION
During the manufacture of fiber suspensions, undesired coarse particles, such as, for example, undefibered material, bark, knots and the like, are present in the suspension as a result of incomplete manufacturing processes. In addition, other impurities, which are both light and heavy, such as plastics, sand and scrap, can also be found in the suspension. In particular, fiber suspensions of slushed return fibers contain great amounts of foreign impurities. Heavy impurities, such as stones, sand and glass, plaster and wire clips, and light impurities, such as certain plastics, agglomerated glue lumps ("stickies") etc., can cause interruptions in the screening process. It is, therefore, desired to separate them at an early stage of the screening process. For this purpose, special devices, for example knot screens or refiners, can be arranged before the screen in order to eliminate the coarse impurities or reduce their size. Light impurities can also be separated by special devices before the screen. It is also possible to separate the coarse impurities by a first screening step in the screening arrangement or to separate scrap and heavy particles when the suspension enters the screen, and other impurities during the fine screening process. In the last mentioned case, the screening process can be disturbed by the impurities, as mentioned above.
During the screening of pulp suspensions it is also desired to have a high pulp concentration, for example, about 3 to 5%, and a low reject draw-off in order to achieve a high production capacity and to avoid unnecessarily large liquid transport in the screening system. High concentration and low reject draw-off, however, imply greater difficulties in separating the impurities from the pulp.
SUMMARY OF THE INVENTION
According to the present invention, the aforesaid problems are solved for designing the screening arrangement for screening the pulp suspension in two integrated steps, where heavy and light impurities can be separated in a first step, and fine screening takes place in a second step.
In accordance with the present invention, these objects have thus been achieved by the discovery of apparatus for screening pulp suspensions containing heavy impurities comprising a casing including a lower end and an upper end and including an inlet for the pulp suspension disposed at the lower end of the casing, a stationary screen mounted within the casing, a rotor mounted for rotation within the stationary screen, the rotor including an inner surface, a lower end and an upper end and forming a screening zone between the rotor and stationary screen, the inlet being disposed within the rotor, the rotor including at least one opening adjacent to the upper end of the casing for transferring the pulp into the screening zone, and a chamber for the heavy impurities disposed adjacent to one of the upper and lower ends of the casing, the rotor including heavy impurity movement means for moving the heavy impurities from the inner surface of the rotor to the chamber.
In accordance with one embodiment of the apparatus of the present invention, the chamber for the heavy impurities is disposed at the lower end of the casing adjacent to the lower end of the rotor.
In accordance with another embodiment of the apparatus of the present invention, the chamber for the heavy impurities is disposed at the upper end of the casing adjacent to the upper end of the rotor.
In accordance with another embodiment of the apparatus of the present invention, the rotor includes a cylindrical surface including strips for guiding the heavy impurities upwardly within the rotor. In a preferred embodiment, the strips are axially disposed along the inner surface of the rotor. In another embod
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patent: 5492225 (1996-02-01), Musselmann et al.
patent: 5622267 (1997-04-01), Hautala
Lithgow Thomas M.
Sunds Defibrator Industries AB
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