Importance

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Abstract

The problems of non-uniform treatment of paper pulp that may be caused by differential flow velocities within a vessel, channeling, and/or disruption of the pulp flow, are substantially eliminated by providing a non-circular cross-section substantially atmospheric pressure vessel with at least one screen surface, and typically a liquid introducing device. The vessel, screen surface, and liquid introducing device are constructed and positioned with respect to each other so that during the treatment of a pulp slurry the slurry has substantially uniform width in a treatment zone, and there is substantially uniform resistance to the flow of slurry over the screen surface over any particular cross-section of the vessel in the treatment zone, and its consistency varies less than 6% in the treatment zone (e.g. between 8-14%). The screen surface may comprise substantially vertical screening portions vertically spaced by non-screening portions, and the vessel wall may bulge out at the location of the non-screening portions so as to provide a slurry width at the bulges at least five percent wider than at the screening portions. The vessel may have a substantially race track shape in cross-section at the treatment zone, and the slurry width may form an annulus in the vessel, the annulus being substantially uninterrupted in the treatment zone (there being no arms or like structures which disrupt the flow). The screen surface may be rotated 5-30.degree., or oscillated or vibrated horizontally (transverse to pulp movement) to minimize plugging.

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First Claim