A. Ahlstrom Corporation

Hannu U Ronkonharju

Olavi E Pikka

Kaj Henricson

Erkki T Repo

An apparatus and method for screening pulp after bleaching. The apparatus includes a first bleaching tower for bleaching pulp, a screener for screening and separating the bleached pulp into a first accept fraction and a first reject fraction such that the first accept fraction is supplied to a post-screening treatment device without further treatment by a separate thickener. The apparatus further includes a vortex cleaner for separating the first reject fraction into a second accept fraction and a second reject fraction such that the second accept fraction is supplied to the screener or the post-screening treatment device without a separate thickener.

Method and arrangement for the treatment of a fiber suspension

A method and apparatus for the treatment of fiber suspensions of the pulp and paper industry, in particular, the so-called postscreening of pulp in the bleaching stage. The method includes that the pulp discharged from a bleaching stage is diluted to the screening consistency, that the pulp is screened in a pressure screen and that the accept fraction is supplied to the subsequent treatment stage at the supply consistency of the stage without a separate thickening stage. The screening is preferably carried out in a narrow-slot screen.

A method of and apparatus for separating knots from a fibre suspension in the wood processing industry. A known problem in the prior art has been the quick wear of the screen surface of the knotter when the screen surface has been profiled. On the other hand the ability to separate with an unprofiled screen has not been satisfactory. When using a profiled screen cylinder (5), it has been noticed in performed tests that it is preferable to feed the pulp from the connections (2) in the direction of rotation of the screen cylinder and also to discharge the reject from connections (4) and the accept from the connections (3) in the direction of rotation of the cylinder (5). Accordingly, there is not only less wear of the screen surface, but also a significantly smaller consumption of power per pulp ton than in the prior art apparatuses.

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Kyminlinna, Finland

Hannu U Ronkonharju