Liquid purification or separation – Filter – Movable medium
Patent
1996-09-20
1998-09-08
Lithgow, Thomas M.
Liquid purification or separation
Filter
Movable medium
210394, 210331, 210332, 21033301, 210334, B01D 3323
Patent
active
058040714
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a rotating filter having a number of filter discs being arranged on a rotor. More precisely, the filter is so designed that the liquid mixture to be filtered is supplied through a hollow shaft of the rotor to the inside of the filter discs, each filter disc being comprised of two side walls with filter means and a wall provided around the periphery, preferably also provided with filtering means.
At the filtration the liquid passes through the filtering means outwards from the inside, whereby a filter layer comprised of solid particles, a coarse phase, is formed on the inside of the filtering means. The filtration takes place with the aid of a hydrostatic overpressure, which is obtained because the liquid level of the liquid mixture inside the rotor is arranged higher than the liquid level of the filtrate outside the filter discs. A disc filter of this type is disclosed in e.g. the U.S. Pat. No. 3,163,601.
The problems of filters having a flow direction from the inside to the outside through the filtering means are that a large part of the filter layer, when this has reached above the pool surface of not filtered liquid mixture, during the rotation falls off and back into the pool. This creates a higher concentration in the liquid mixture coming in and thereby the technical performance of the filter is deteriorated, i.e. its capacity in different aspects, such as the hydraulic capacity, the amount of separated solid particles and/or the purity of the filtrate.
SUMMARY OF THE INVENTION
The object of the present invention is to increase the capacity of the filter. This results in that, at a given incoming flow a smaller filter area and thereby smaller filter units are required.
According to the present invention, in the inside space of the filter discs, carrier elements for the filtered coarse phase as well as blocking means for preventing this coarse phase to fall back down into the pool of the incoming liquid mixture, are provided. These blocking means will in the following be called barrier elements. By preventing coarse phase from being filtered once more and thereby occupying filter area the capacity of the filter is increased.
A filter according to the present invention is well adapted for purification of sewage water, raw water, so called back-water in the paper industry and for fibre recovery in the paper industry.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention, having the characteristics according to the appended claims, will be described more in detail in the following with reference to the appended drawings, in which
FIG. 1 shows a cross section (I--I in FIG. 2) of a filter,
FIG. 2 shows a longitudinal section (II--II in FIG. 1),
FIG. 3 shows the invention in a sector of a filter disc,
FIG. 4 shows an alternative embodiment of the invention,
FIG. 5 shows, in a cross sectional view, a lateral surface of a filter disc (V--V in FIG. 6),
FIG. 6 shows, in an enlarged scale, a section (VI--VI in FIG. 5) of the lateral surface,
FIG. 7 shows an alternative embodiment of the invention,
FIG. 8 shows a modification of the embodiment in FIG. 7.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
FIGS. 1 and 2 show a principal embodiment of a disc filter. This comprises a filter rotor 1 placed in a filter vessel 2 for the filtrate. A hollow shaft 3, on which filter discs 4 with filtering means are arranged, is rotated in the vessel with the aid of a driving means 5. The filter means in their simplest embodiment are comprised of a filter cloth braced on a supporting underlayer so that an inside space 6 is formed. The filter cloth embraces both sides of the filter discs and preferably also the outer periphery 7. The inside of the filter discs communicate with the hollow shalt 3. The liquid mixture to be filtered is introduced in the hollow shaft through the inlet 8 and thereby also to the inner space 6 of the filter discs. A means according to known technique, not shown, sees to that a substantially constant level is maintained in the shaft and in
REFERENCES:
patent: 1712258 (1929-05-01), Compain
patent: 2765915 (1956-10-01), Nilsson
patent: 2891671 (1959-06-01), Nilsson
patent: 3163601 (1964-12-01), Ericson
patent: 3278039 (1966-10-01), Nilsson
patent: 4724077 (1988-02-01), Uchiyama
patent: 5667680 (1997-09-01), Haeffner
Lithgow Thomas M.
Nordic Water Products AB
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