Liquid purification or separation – Plural distinct separators – Filters
Patent
1989-10-03
1991-07-16
Woo, Jay H.
Liquid purification or separation
Plural distinct separators
Filters
210327, 210346, 210486, B01D 3321
Patent
active
050322702
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a thickener, i.e., an apparatus for raising the dry solids content in suspensions, such as fiber suspensions, by means of filtering. Such an apparatus includes a plurality of rotatable filter disks mutually spaced in axial direction and adapted to be partially submerged in a liquid or a suspension to be filtered, each disk comprising a plurality of filter sections communicating with axial ducts arranged at the outer peripheries of the filter disks for removal of filtrate.
BACKGROUND OF THE INVENTION
Apparatuses of this kind are known, inter alia, from SEC-C-8305817-2 (corresponding to EP-B1-0160069 and U.S. Pat. No. -4 634 529) and have the advantage of combining a very large filter surface with a relatively small volume. However, when it comes to achieving thickening of a fiber suspension, i.e., raising the dry solids content from typically 0.5% to typically 5%, very high capacity, i.e., a large filtrate flow through the apparatus, is required. One way of increasing the flow capacity is to increase the rotation rate. However, a high rate of rotation means that the filter sections do not have time to be emptied of filtrate before the sections reach the position where the filter cake is to be removed. The reason for this is that the filter cake that is built up has time to be too dense to pass through sufficient air to replace the filtrate flowing out. It can thus occur that the filtrate wets the filter cake remaining on the filter section, or that the filtrate together with the filter cake runs down into the collection vessel intended for the filter cake. This phenomenon is usually referred to as re-wetting or "backwash". The known apparatuses are moreover expensive to manufacture, inter alia because they require a vacuum valve and a vacuum source for establishing a sufficiently large pressure difference between the suspension and the filtrate discharge duct.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a thickener apparatus which allows a high rate of rotation and hence high capacity, and which does not require an outside vacuum source, but is thus simple and cheap in manufacture.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the accompanying drawings, wherein several embodiments are shown for purposes of illustration, and wherein
FIG. 1 is a cross section through a thickener with a plurality of annularly arranged filter sectors,
FIG. 2 is an axial section through the thickener according to FIG. 1,
FIG. 3 is an enlarged detail of a filter rotor of a thickener according to FIG. 1, and
FIG. 4 is an axial section through a further embodiment of the thickener according to the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
A thickener in accordance with the invention includes a filter rotor having a plurality of annular filter disk holders 1 arranged axially in sequence, and filtrate ducts 2 axially connecting the holders 1. FIG. 1 is a cross section through such a filter rotor, which is rotatable counter-clockwise as seen in the figure, and which carries an annular filter disk 3 comprising a plurality of filter sections 4. The interior of each filter section 4 is in communication with an associated axial filtrate duct 2, namely, the closest trailing filtrate duct 2 in the direction of rotation. All the filter disks of the filter are partially submerged in the liquid or suspension 5 to be thickened (filtered) and which is received in a container 6. The container 6 rests on a foundation 7,8. Through the central opening of the filter disks extends a collecting trough 9 for solid material, such as cellulose fibers, which are deposited on the filter sections during thickening and are caused to fall optionally with the aid of a jet 10, from the filter sections when they are above the trough 9. An oscillating spray means 11 may be provided for washing off particles from the filter sections. The structure also includes an inlet 12 for suspension and a casing 13 over the rotor,
REFERENCES:
patent: 4056473 (1977-11-01), Nilsson
patent: 4634529 (1987-01-01), Nilsson
patent: 4678574 (1987-07-01), Niiranen et al.
patent: 4781835 (1988-11-01), Bahr et al.
patent: 4814093 (1989-03-01), Frykhult
Nilsson Bjarne
Nilsson Harry
Mackey James P.
Woo Jay H.
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