Method and device for handling cellulose pulp

Abstract

The invention concerns a method and a device for the dilution of dewatered cellulose pulp that maintains a consistency of 30% or greater. By shredding of the pulp to a finely divided dry granulate, dilution to a homogeneous consistency in the medium consistency range can take place exclusively through hydrodynamic effects from the addition of dilution fluid. The dilution fluid is added to the granulate at a position at which the granulate is in free fall in a stand pipe 22, 40 and above a level LiqLEV of diluted pulp in the stand pipe. A number of nozzles are arranged around the periphery of the stand pipe, directed in towards the centre of the stand pipe, obliquely downwards in the direction of fall of the granulate. It is possible through this simplified procedure to avoid completely the conventional dilution screws, and this reduces the investment costs and is operating costs, while at the same time unnecessary mechanical influence of the pulp fibres can be avoided.

Description

[0001] The present invention concerns a method according to the preamble of claim 1 and a device according to the preamble of claim 4. THE PRIOR ART [0002] In association with either one of the bleaching and the delignification of cellulose pulp in bleaching lines, the pulp passes between different treatment steps in which the pulp is subjected to bleaching or the delignifying effect of various treatment chemicals. The treatment typically alternates between alkaline and acidic treatment steps in which typical sequences may be of ECF type (elemental chlorine-free, Cl, in which chlorine dioxide may be used) such as O-D-E-D-E-D, O-D-PO or sequences of TCF-type (totally chlorine-free) such as O-Z-E-P. Other bleaching steps, such as Pa steps and H steps may be used. [0003] The treatment steps may take place either at medium consistency (8-16%) or at high consistency (≧30%), but it is vitally important to wash out after each treatment step degradation products and lignin precipitated duri...

AI Technical Summary

Problems solved by technology

A consistency higher than 8-14% is generally never achieved for the pulp bed that has been dewatered, due to the limited degree of dewatering that is achieved, and the dewatered pulp that is scraped of can be readily formed to a slurry with a low consistency again in a subsequent collecting trough.

A practical upper limit lies at 35-40%, where a higher degree of dryness cannot be achieved without affecting the strength properties of the fibres negatively.

Acidic conditions require material that can resist acids, and this is significantly more expensive that other material.

The use of a dilution screw at this position, however, increases the requirement for energy, it increases investment costs, it raises the requirement for maintenance and it involves a further mechanical treatment of the pulp which has a negative influence on the strength properties of the pulp.

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