Liquid purification or separation – Plural distinct separators – Filters
Patent
1992-08-26
1993-12-28
Dawson, Robert A.
Liquid purification or separation
Plural distinct separators
Filters
210404, 210486, B01D 3309
Patent
active
052736512
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns an arrangement in a disc filter including at least one filter disc partly submerged in a vessel for liquid or suspension to be filtered, said filter disc including a plurality of substantially annularly disposed filter sectors and being rotatable about a collecting trough for solid substance deposited on the outside of the filter sectors and falling down therefrom, each filter sector having a filtrate outlet by means of which the interior of the filter sector communicates with an axial channel for discharge of filtrate, and said filtrate outlet being arranged at the edge of the filter sector trailing upon rotation of filter disc and being connected to the side of the axial channel leading in the direction of rotation.
Filters of this kind are mainly used in cellulose and pulp industry for thickening fiber suspensions and for cleaning process water, so called fiber recovery.
For such use large filter areas are necessary and, thus, filters comprising several parallel filter discs are common.
Of the kind initially stated there have hitherto existed two main types.
In the first, older type, described in U.S. Pat. No. 4,056,473, the axial channels are centrally arranged and form, together with cross-channels extending between the axial channels, part of the annular rotor surrounding the collecting trough. The filter sectors, being carried by and communicating with each one cross channel in turn communicating with an axial channel, extend substantially radially and approximately fan-like outwards from the rotor. On one hand the rotor must have a certain minimum diameter to accommodate an appropriate collecting trough, while on the other hand as small a rotor diameter (i.e., the inner diameter of the filter disc) as possible is desirable to obtain the largest possible filter area without the outer diameter of the filter disc becoming much too large. Particularly when there is a small central opening in a filter disc of this kind the problem exists that solid substance falling down from the filter sector may be entirely or partly hanging on the axial channel trailing in the direction of rotation, since the axial channels, due to the shape of the filter sectors tapering towards the center, are relatively closely arranged. In order to overcome this problem it has been suggested, according to SE-B8301652-7, corresponding to U.S. Pat. No. 4,678,575, that the axial channels be arranged in groups of at least two and that adjacent filter sectors shall communicate with one each of these axial channels by each one cross-channel. Although hereby has been created a greater space between adjacent groups of axial channels this is still not enough to ensure that solid substance falling from the filter sectors shall avoid to be trapped on the axial channels. Further, from a purely constructional and manufactural point of view, the grouping of the axial channels as well as the connection of the cross-channels to the axial channels make a filter of this kind both complicated and expensive.
In the other kind of filter, represented by the filter according to SE-B-8305817-2, corresponding to U.S. Pat. No. 4,634,529 and EP-B1-016069, the axial channels are arranged at the outer circumference of each filter disc. Hereby, the central opening of the filter is entirely free from every obstacle for solid substance falling from the filter sectors. In practice, and according to SE-B-8702620-9, corresponding to WO 88/10144, such a filter is also made with cross-channels comprising sections of an annular channel arranged at the outer periphery of a filter disc, each such section communicating with an axial channel. One problem with filters of this second kind is that the rotor diameter becomes very large when a great filtering capacity is desired, which, in practice, puts a limit to the largest diameter of the filter disc and thereby for great filtering capacities, particularly for transport reasons.
A combination of the two filter types mentioned, i.e, provision of a filter having filter sectors extending radial
REFERENCES:
patent: 4056473 (1977-11-01), Nilsson
patent: 4634529 (1987-01-01), Nilsson
patent: 4678575 (1987-07-01), Frykhult
patent: 4931179 (1990-06-01), Nilsson
Dawson Robert A.
Millard W. L.
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