Classifying – separating – and assorting solids – Sifting – Drum sifters
Patent
1998-10-29
2000-10-17
Olszewski, Robert P.
Classifying, separating, and assorting solids
Sifting
Drum sifters
209 17, 209283, B07B 120, B07B 106, B03B 700
Patent
active
06131742&
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a device for separating contaminants from a fibre pulp suspension, comprising a hollow housing with two opposite side walls, a substantially cylindrical screen member extending in the interior of the housing from one of the side walls towards the other side wall and dividing the interior of the housing into a first chamber for suspension to be screened by means of the screen member and a second chamber for receiving screened suspension. The device further comprises a rotor in the screen member arranged rotatable about an axis which is coaxial with the screen member, and a tubular wall extending in the first chamber from the screen member substantially coaxially with the axis of the rotor towards the other side wall to an open end of the tubular wall situated at a distance from the other side wall. The first chamber has a substantially cylindrical circumference surface extending axially along the tubular wall to the other wall and which is coaxial with the axis of the rotor, whereby an annular inlet passage is formed between said circumference surface and the tubular wall. There are an inlet member for suspension to be separated arranged to conduct the suspension into the inlet passage, a first outlet member adapted to catch relatively large and heavy contaminants moving along said circumference surface in the inlet passage, a second outlet member for discharging screened suspension from the second chamber, and a third outlet member for discharging contaminants from the interior of the screen member.
A separation device of this kind is known from U.S. Pat. No. 4,234,417 and is preferably used for separating relatively coarse contaminants from pulp suspensions. In certain kinds of heavily polluted pulp suspensions, especially such suspensions which are produced from waste paper, there may be very coarse contaminants, such as metal scrap and gravel, which may damage the screen member rotor of the known device. Such very coarse contaminants are therefore separated from the pulp suspension with the aid of a separation stage comprising hydrocyclones, before the pulp suspension is supplied to the known device. The fibre concentration of the pulp suspension is kept at about 0.5% to about 1%, in order to achieve a well functioning hydrocyclone separation. The separation efficiency and capacity of the known device on the other hand is best if the fibre concentration of the pulp suspension is from about 3.5% to about 5%. The fibre concentration of the pulp suspension which leaves the hydrocyclone stage of course may be increased to a suitable concentration with the aid of a dewatering device before the pulp suspension is supplied to the known device. However, this would result in significant increases of costs, and consequently the pulp suspension usually is supplied to the known device directly from the hydrocyclone stage without a preceding dewatering, in spite of the fact that the known device as a result thereof can not function optimally.
The object of the present invention is to provide an improved separation device of the kind here presented with respect to separation of such very coarse contaminants which normally is performed by hydrocyclones.
This object is obtained by means of a device of the kind initially described, which is characterized in that a low deflecting wall member extends from the other side wall towards the rotor to a position in which the wall member is axially substantially in front of the open end of the tubular wall and radially inside the tubular wall, and that the wall member is arranged such that an annular flow passage is formed between the tubular wall and the wall member with a cross-sectional area which is substantially smaller than the cross-sectional area of said annular inlet passage. Hereby the flow velocity of the suspension in the inlet passage will be substantially less than the flow velocity of the suspension through said annular flow passage, which results in that very coarse contaminants entering the inlet passage are efficiently catched b
REFERENCES:
patent: 5078859 (1992-01-01), Satomi
GL&V/Celleco AB
Martin Brett C
Olszewski Robert P.
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