Screening apparatus for separating light impurities from pulp su

Classifying – separating – and assorting solids – Plural – diverse separating operations – Aqueous suspension and sifting

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Details

209273, 209306, 210413, B03B 700

Patent

active

058993380

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to an arrangement for separating light impurities from pulp suspensions in which light impurities are understood to be particles or aggregates with a lower density than water, such as plastic particles. Aggregates are found, for example, during flotation where a heavy particle is bound to a gas, and the aggregate particle/bubble behaves light a light particle.


BACKGROUND OF THE INVENTION

Heavy impurities in pulp suspensions are generally separated with conventional screens by means of centrifugal force in separate scrap taps, while coarse fiber fractions and impurities are generally separated by a screen member whereby the pulp is divided into accept and reject portions.
Light impurities are more difficult to separate, especially at high pulp concentrations. The pulp concentration, however, is desired to be high, for example, from about 3 to 5%, in order to achieve a high production capacity and to avoid the transport of large liquid volumes in the screening system.
Light impurities, therefore, are usually separated in separate devices, such as hydrocyclones. This requires not only separate equipment, but also low concentrations, below about 1%, in order to achieve a good result. It is, therefore, a less attractive method to vortex clean the entire flow from a pulp line. Instead, it is possible to carry out pressure screening through very fine slits at the highest possible concentration, and thereafter to use a vortex cleaner for separating the light impurities from the reject flow from the screens.


SUMMARY OF THE INVENTION

In accordance with the present invention a solution for the aforesaid problems has been provided, in that a device for removing light impurities is designed to be directly connected to the casing of a fractionation means, for example a conventional screen arrangement.
In accordance with the present invention, apparatus is provided for separating light impurities from a pulp suspension which is treated in a fractionation device having a casing with an upper portion for breaking up the fibrous network of the pulp suspension and for rotating the pulp suspension about an axis of rotation within the casing in order to enrich the light impurities therein, the apparatus comprising a housing having an upper portion and a lower portion symmetrically disposed with respect to the axis of rotation of the casing, and a passageway extending between the lower portion of the housing and the upper portion of the casing, the housing including an outlet for the light impurities located at the upper portion of the housing, and a dilution liquid inlet connected tangentially to the housing for injecting a dilution liquid into the housing.
In accordance with one embodiment of the apparatus of the present invention, the lower portion of the housing includes an upwardly diverging configuration and the upper portion of the housing includes a substantially cylindrical configuration.
In accordance with another embodiment of the apparatus of the present invention, the dilution liquid inlet is located between the upper and lower portions of the housing.
In accordance with another embodiment of the apparatus of the present invention, the housing includes an intermediate portion between the upper portion of the housing and a lower portion of the housing, the location of the intermediate portion of the housing being determined by the flow characteristics of the location of the dilution liquid inlet.
In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a valve associated with the outlet for controlling the discharge of the light impurities therefrom.
In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a rotor axle extending through the passageway into the housing, the rotor axle including a rotor element for effecting rotation of the contents within the housing. In a preferred embodiment, the rotor axle includes a screw thread for effecting upward feeding of t

REFERENCES:
patent: 4107033 (1978-08-01), Holz
patent: 5318186 (1994-06-01), Rienecker

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