Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Patent
1991-02-12
1993-01-05
Jones, W. Gary
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
162 56, 162 23, 162 52, D21B 108
Patent
active
051767937
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of treating wood-fiber pulp, particularly pulp which contains waste or recycled paper.
According to another aspect, the invention relates to a disperger or disperser for finely-dividing wood-fiber pulp.
When treating such pulp in accordance with conventional techniques, the pulp is processed in a plurality of treatment stages, including dewatering of the pulp in a dewatering zone by means of a screw-press, so as to increase the pulp consistency from an input value of from 4-6% to an outgoing value of about 30%.
The pulp is passed from the dewatering zone to a heating zone, in which the pulp is advanced while steam is supplied to the zone. The pulp is processed in this zone by means of a so-called pulp shredder, which converts the pulp into granules or small particles or some like form, so as to enable the pulp to be heated quickly and uniformly to the temperature desired with the aid of saturated steam. The average steam consumption is about 300 kg/ton pulp.
The heated and finely-divided pulp is then passed to a disperser, which enables the pulp material to be worked gently at high consistencies. This is made possible by the mutually opposing toothed disks of the disperser, of which one disk rotates relative to the other. The dispersion-gap is adjusted during operation, suitably by means of an electro-hydraulic system.
The temperature of the pulp processed may be varied between, for instance, 80.degree. and 120.degree. C., depending on the nature of the pulp being processed. The fibers present in the pulp are liable to be destroyed or damaged when excessively high temperatures are used.
The pulp exiting from the heating zone may have a consistency of up to 30%. This consistency is reduced to some extent by the pressurized steam delivered to said zone.
Diluting or thinning water is normally added during the dispersion process, and the consistency of the pulp pumped from the disperser will consequently lie between 3.5 and 6%. The pulp consistency, however, may be as high as about 10% in some cases.
Somewhere above 12-13% lies a limit at which it is no longer possible to pump the pulp with the aid of present day techniques.
There are many instances, however, when pulp of higher consistencies are required, where values of 25-30%, or still higher, may be strived for. Such consistencies, however, are not possible to achieve with the aid of pulp-processing methods hitherto applied.
At the same time, there is a desire to increase the temperature and/or the pressure of the steam supplied, this desire being particularly manifest in those instances when pulped highly-contaminated recycled paper is processed.
Difficulties are encountered, however, in recovering the heat-content of steam effectively. For instance, there is a risk that the steam will be blown from the system and consequently not utilized to the fullest.
Examples of the present state of this art are found in SE,B,435 532 and FI,B,66927 (both Sunds Defibrator) and FI,B,58171 (Keskuslaboratorio). In the case of these known methods and apparatus, the steam is removed and discharged through separate steam outlets, so as to enable the steam to be re-used.
None of these known methods relates to the treatment of pulp containing recycled paper, particularly highly-contaminated paper.
SUMMARY OF THE INVENTION
A prime object of the present invention is to provide an improved method for the treatment of wood-fiber pulp which will enable the heat-content of the steam supplied to the heating zone to be utilized in a nore efficient manner, thereby to enable highly-contaminated recycled paper to be treated more effectively, and to increase the pulp consistency of the treated final product.
A further object is to provide a treatment method which can be adapted to prevailing parameters of the treated product with the aid of simple means, and which will provide a good result when the temperature prevailing during the treatment process varies between values which lie beneath and substantially above 100.de
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Cellwood Machinery AB
Jones W. Gary
Lamb Brenda
LandOfFree
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