Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With agitation or forced circulation
Patent
1996-05-23
1997-11-18
Czaja, Donald E.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With agitation or forced circulation
162246, 162 60, 162 55, 162 52, 68181R, 8156, D21C 910, D21C 708
Patent
active
056883692
DESCRIPTION:
BRIEF SUMMARY
This Application is filed under 35 USC 371 of PCT/SE094/01022 filed Nov. 2, 1994.
TECHNICAL FIELD
The invention concerns the cellulose technique and relates to a method for feeding out fibre pulp over an overflow rim at the upper end of a cylindrical container through which the pulp, which is suspended in a liquid, is being fed continuously from the bottom and upwards. The invention also relates to a device for, at the upper end of the cylindrical container through which the suspended fibre pulp is being fed continuously upwards, feeding out the fibre pulp over the overflow rim and also diluting the pulp to a concentration which is desired for the subsequent treatment.
BACKGROUND TO THE INVENTION
Many processes within the cellulose production technique are carried out using pulp concentrations of the order of size of 10%, so-called MC pulp. This is the case, for example, for a number of bleaching techniques. Whereas this concentration of medium magnitude is very suitable for the bleaching process, it is not appropriate, for example, for subsequent washing stages in the form of washing presses and filters.
In accordance with the current technique, the fibre pulp is fed out, with the aid of scrapers, over an overflow rim at the upper end of the bleaching tower. At this point, the pulp normally has a concentration of from 8 to 10% and is thus far from being of low viscosity. This means that it forms more or less connected lumps when it is driven out by the scrapers into a channel, a so-called launder, outside the overflow rim. In the launder, diluting nozzles are located through which liquid, usually water, is supplied to the pulp in the launder so that the fibre pulp will assume the form of a suspension having the desired fibre concentration. However, there can be no certainty that the pulp suspension will be well homogenized, since no mechanical agitation is carried out.
It is also known to supply diluting liquid through nozzles over the surface of the fibre pulp at the top of the bleaching tower, but this does not solve the homogenization problem in a satisfactory manner, since liquid and fibre pulp do not have time to become mixed with each other and be well homogenized, before the scrapers drive the pulp out towards and over the overflow rim.
It is also known, from the diffuser technique, to supply washing liquid via nozzles to a diffuser at a substantial depth below the outfeed scrapers. An early example of this technique is described in SE 225 814. However, in this case, it is simply a question of supplying washing liquid which is taken up by the diffuser and conducted away through the latter, implying that no dilution of the fibre pulp which is being fed upwards through the cylindrical container takes place.
Another known diffuser technique is also to dilute pulp using diluting nozzles secured to a rotating arm, but the arm is then submerged in the pulp and is not provided with scraping blades.
BRIEF ACCOUNT OF THE INVENTION
The object of the invention is partly to facilitate the feeding-out of pulp over an overflow rim at the upper end of a cylindrical container, through which the pulp, which is suspended in a liquid, is being fed continuously from the bottom and upwards, preferably feeding-out of fibre pulp at the top of a bleaching tower, partly to dilute the pulp to a substantial degree, and partly to bring about an efficient homogenization of the fibre pulp and diluting liquid.
These and other objects can be achieved by the pulp being diluted at a level below the surface of the pulp through a multiplicity of nozzles, which are submerged in the pulp and which are rotated around the vertical centre line of the container, with so much diluting liquid that the quantity of liquid in the layer between the nozzles and the upper surface of the fibre pulp suspension is increased by at least 50%, preferably by at least 100%, and by the pulp, which has been fed upwards through the container, and the diluting liquid being thoroughly mixed with each other, to form an essentially homogeneous suspensio
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Landmark Lars
Nilsson Mikael
Czaja Donald E.
Fortuna Jose S.
Kvaerner Pulping Aktiebolag
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