Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Mechanical defibration in the presence of heated gas or gas...
Patent
1979-10-17
1982-11-02
Chin, Peter
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Mechanical defibration in the presence of heated gas or gas...
162 25, 162 28, D21B 112
Patent
active
043572081
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of making refiner pulp of high yield (>85%) by refining lignocellulose-containing material such as chips, sawdust or defibred chips. The material is preheated and/or treated with lignin-softening chemicals prior to the refining, which usually is carried out in disc refiners.
At conventional embodiments of the refining process the fibre material is refined at very high fibre concentrations, in such a manner, that the amount of water supplied to the refiner is held at the lowest possible level. This is necessary for obtaining good properties of the exposed fibres and for rendering them suitable for the manufacture of a series of different paper qualities. The refining process, however, requires much energy. Therefore, in view of the ever increasing energy prices and the restricted energy supply it is increasingly disadvantageous to make mechanical or chemi-mechanical pulps of the above yields by this process.
It was, however, found very surprisingly that it is possible by the present invention to substantially reduce the energy consumption at the refining without abandoning the quality of the resulting pulp. In certain cases even an improvement of the quality was observed.
The fibre material is decomposed at the refining to fibres or fibre fragments while the material is passing through the narrow gap between the refining segments in the disc refiner. As regards the process parameters, such as pressure, temperature, concentration, production, refining disc pattern etc. in the refiner, it is essential to choose them so as to obtain a gap of adequate size at the desired effect input and processing of the fibre material. Too narrow a gap implies difficulties for the pulp transport through the gap and often results in a poor pulp quality because many fibres during their passage between the discs are cut off or damaged in cessing of the fibre material is not obtained during a single passage, but the refining operation must be repeated two or more times with the entire pulp amount or with a part thereof, i.e. the refining must be carried out in several steps. The steam, besides, occupies a vary large part of the space in the gap between the operating refining discs. For this reason, and because the fibre material at high concentraions is not distributed uniformly in the gap and over the refining segments, the possibilities offered by the refining segments cannot all be utilized for processing the fibre material.
Although the greater part of the steam formed flows out at the periphery of the refining segments, a non-neglectible part thereof flows back and out of the refiner where the chips are being fed in. This feed, of course, is obstructed thereby, which gives rise to serious effect variations. Such a varying fibre flow through the refiner, of course, has a detrimental effect on the pulp quality. When the fibre flow is too great, the fibres are refined insufficiently, and when the flow is too small, the fibres will be refined much too intensely.
The steam flow, partially in forward and partially in rearward direction, is due to the fact that the pressure in the gap between the refining segments increases with increased energy transfer in the direction to the periphery and reaches a maximum somewhere in the outer part. The energy transfer and the steam formation are here at their maximum, and this area constitutes a natural divider for the forward/rearward steamflow.
Thus, great steam amounts difficult to manage are formed when the refining of fibre material must be carried out at high fibre concentrations. The fibre concentrations, determined immediately after the refining, mostly are in the range of 25-35%. The steam problems, therefore, determine to a high degree the design of the disc segments, i.e. of the instruments applied to refining the fibre material. Grooves and ridges, thus must be formed so that the grooves are sufficiently wide and deep for not obstructing the steam transport. Often, on the other hand, a narrower groove and a wider ridge would be more advantageo
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patent: 4166584 (1979-09-01), Asplund
Hoglund Hans E.
Peterson Per V.
Chin Peter
Sca Development Aktiebolag
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