Classifying – separating – and assorting solids – Sifting – Feeding
Patent
1995-10-16
1999-03-16
Terrell, William E.
Classifying, separating, and assorting solids
Sifting
Feeding
209380, 210327, 210391, 19204, B07B 108, D21D 502
Patent
active
058818871
DESCRIPTION:
BRIEF SUMMARY
1. FIELD OF INVENTION
The invention concerns removal of fibre fragments, fibre fines and other particles from fibre suspensions, for example suspensions formed during the production of pulp and paper.
Fibre fragments, fines and other, minor particles are often undesired in fibre suspensions due to the fact that they hinder paper drainage in the paper machine and thereby reducing the machine's production capacity. Also, fibre fragments and fines in the finished paper reduce the strength of the paper and cause unwanted dusting from the paper web in printing shops.
Fragments and fines also often cause delamination of the paper sheet, which again leads to paper rupture.
Fibre fragments, etc. reduce the paper quality, and may, under circumstances, make the fibre suspension unsuitable for paper production.
These problems are exacerbated by increased consumption of secondary fibres because new fibre fragments and new fines are created from secondary fibres every time they are re-used for the production of paper.
Therefore, there is a great and steadily increasing demand for a suitable apparatus capable of fractionation of fibre suspensions for separating fibre fragments, fines and other, unwanted small particles from fibre suspensions.
Due to the more stringent environmental regulations there will be an increased demand for separation of suspended solids from liquids, in other fields as well.
In addition, the invention is generally applicable for the recovery of fibres and solids from suspensions.
2. STAR OF TECHNOLOGY
The machinery used today for the separation of fibres, fibre fragments and fines from fibre suspensions are constructed as bow screens or as rotating drum- or disc filters.
These filters have various designs and modes of operation, and are less suited for fibre fractionation.
The filtering area of the bow screen consists of many, parallel metal rods packed together at certain, internal intervals, thus forming a relative. smooth filtering surface, whereby the intervals between the rods constitute the perforation or open area of the filtering surface. The filtering areas of the drum- and disc filters are woven clothes of high mesh, usually made out of monofilament threads of synthetic material (plastics), the filtering area rotating slowly within a vat filled with the suspension to be filtered.
The static bow screen functions with the fibre suspension flushing over the filtering area, across the metal rods and their intervals, either by having the suspension flushing over an inclined, bowed surface by its own momentum or being sprayed onto the filtering surface, approximately tangential to the bow's form.
During rotation of the drum and disc filter in the fibre suspension a filtering layer consisting of fibres is formed on the one side of the high-mesh screen cloth through which the filtrate is penetrating. This filtering layer, formed onto the the filtering cloth, consists of fibres from the suspension to be filtered, or can be added to the suspension beforehand, as a so called filtering pulp. With each revolution of the drum- or disc filters, this filtering layer, which contains those fragments and those fines which has been filtered out of the suspension, is washed off the filtering cloth by means of water or air. This filtering layer retains not only the fibres but also fibre fragments and fines. Both drum- and disc filters are therefore suited for socalled barrier screening of fibre suspensions, but less suitable for the fractionation of same.
Due to its relatively coarse, mechanical construction and coarse perforation, the bow screen is not suited for fractionation, as the screen permits too many usable fibres to slip through together with the fragments and the fines which should be separated from the fibre suspension.
3. BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the screening material of the present invention.
FIG. 2 illustrates aspects of the screening system of the present invention.
FIG. 3 illustrates the screening material as a plate.
FIG. 4 illustrates the apparatus as a
REFERENCES:
patent: 2988223 (1961-06-01), Janson
patent: 4696751 (1987-09-01), Eifling
patent: 5124029 (1992-06-01), Fjallstrom et al.
International Search Report dated Dec. 9, 1993.
Nguyen Tuan N.
Terrell William E.
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