Bleaching and dyeing; fluid treatment and chemical modification – Fluid treatment – Special forms and forming
Patent
1995-06-30
1997-12-23
Stinson, Frankie L.
Bleaching and dyeing; fluid treatment and chemical modification
Fluid treatment
Special forms and forming
68181R, 162 60, D06B 502
Patent
active
056995733
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a pulp washing method used to remove chemicals dissolved in liquids, for example in connection with chemical or mechanical pulp washing or bleaching processes, or to replace the chemicals contained in a liquid. The invention also relates to a pulp washing machine for carrying out this method.
BACKGROUND OF THE INVENTION
The known washing methods belong to the categories of diffusion washing, displacement washing, and pressing. Diffusion washers often are drum filters, boosted either by vacuum or pressure. A displacement step using showers is often added to them. Displacement washers, are either drums, wire machines or towers. In all washers, the washing liquid generally moves in the counter-current direction in relation to the pulp to be washed. The desired washing water consumption is 2 to 2.5 cubic metres of water per one dry pulp ton. In order to reach a sufficiently good washing result, for example, four washing filters in series, or a multiphase drum displacement washer are often used. In principle, washing presses operate like pressure filters, than is to say, they remove liquid from pulp by pressure. Usually, these washing presses are either of a screw or a double roll type, but also drum presses have been tried.
Modern displacement towers and displacement drums are very efficient washing machines and they can cope with the total washing needs of the production line, even alone, but, on the other hand, they also are very expensive and large units.
Due to their high prices and big sizes, displacement towers and displacement drums are not well suited for improving the efficiencies of existing washing lines. Washing filters can always be added in series to the line, but even this is relatively expensive and it also requires the installing of diluting devices and, in addition to this, the configuration as a whole will then form a relatively large unit.
Washing presses are often used to enhance the existing washing lines. However, the most efficient of the known presses suitable for this purpose, the screw presses, cut so much of the fibers when kneading them under pressure against the perforated housing and the screw flange that they cannot in general be used in the production of high quality chemical pulp. Double roll presses again are expensive but, on the other hand, very efficient devices by which an approximately 1 per cent pulp can be dried to an about 40 per cent dry matter content.
The one-phase drum presses used to press pulp do not break the fibers and they would be suitable, also as far as their prices are concerned, to enhance the existing washing lines but they have not appeared efficient even when improved by a displacement step brought about by pumping. Pumping washing liquid evenly through a pressed pulp layer has turned out to be difficult and inefficient, and most often the displacement step has been omitted.
SUMMARY OF THE INVENTION
The object of the invention is to eliminate these difficulties, that is to say, to create a simple, very reliably operating and sufficiently efficient washing device that will not break fibers and, despite of that, is so cheap that it can be used to enhance existing washing lines. Further, the aim of the invention is the possibility to use the washing device in special situations as a press to dry pulp, for example, for provisional storage.
The idea of the invention is to use the press for drying wood wastes, known as such, so that a detergent is fed to the pulp once or several times as it is running through the rotating drum, between the drum and the pressing roll inside it.
The basic machine can, for instance, be a press according to Finnish Patent 62330. According to the invention, washing liquid feeding means will be added to the machine in suitable positions along the pulp feeding track. The detergent is advantageously fed to the pulp after every pressing step, whereafter washing liquid and all solid materials diluted in it will be removed by the next pressing step. Feeding the liquid to that side of the pulp layer that
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Finbark Oy
Stinson Frankie L.
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