Classifying – separating – and assorting solids – Sifting – With liquid treatment
Patent
1996-08-05
1998-09-15
Terrell, William E.
Classifying, separating, and assorting solids
Sifting
With liquid treatment
209284, 209288, B07B 122
Patent
active
058066845
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns a fractionator for fractioning a suspension in at least two fractions, including a drum rotatable about a substantially horizontal axis and having axially spaced end walls, a centrally arranged inlet for suspension, a flow channel for suspension in the drum and outlet means for fractions.
BACKGROUND OF THE INVENTION
Within the pulp industry there is a need to separate from certain filtrates particles accompanying the filtrate, for instance in the manufacture of recycled paper pulp. In one phase of this process, the recycled pulp is washed, which results in that particularly fillers, such as clay and ash, printing ink and so-called fines are washed out of the pulp in a filtering process, which aims at retaining mainly long fibers. However, it is unavoidable that also long fibers accompany the filtrate, which, thus, will contain long fibers, fines, fillers and printing ink. It is, of course, desirable to be able to recover not only the valuable long fibers, but also fines and fillers, of which particularly the latter are valuable and are needed in papermaking. Besides, for environmental reasons it is favourable if also the finest particles can be recovered and recycled.
In order to separate particles of different sizes in a liquid, it is known to utilize a so-called fractionator. A known such fractionator utilizes a rotatable cylindrical drum, which is internally provided with a helical or spiral channel. This channel has a centrally located entrance and an exit located at the periphery of the drum. The suspension to be fractionated is introduced at the centre of the drum, and the drum is rotated so that the entrance end of the helical channel is filled like a scoop with suspension at each revolution. Between two adjacent channel walls, thus, there will be a suspension plug moving outwards towards the outer loop of the helix and the exit of the channel. Thus, between the channel walls and the suspension plug there will take place a relative movement. As is known from the science of flow this results in that larger particles will gather at the front end of the plug, whereas gradually smaller particles will gather gradually further backwards in the plug, all as counted in its relative direction of movement. Seen in the direction of rotation of the drum, thus, the smallest particles are located foremost and the largest last in the plug. Beneath the drum there are two or more collecting means, which are located in a row after and against each other in the rotational direction of the drum. When a suspension plug is situated in the last turn of the helical channel, the entire plug leaves the exit of the channel in a substantially coherent state when the exit moves over and past the collecting means, the plug falling down towards the collecting means. Thus, in the first collecting means, as counted in the direction of rotation of the drum, the largets particles will be caught, while the smallest will be caught in the last collecting means.
This known fractionator has an inherent drawback in that it operates intermittently, since feeding of suspension and discharge of fractions occurs but once a revolution. Further, the fractioning distance, i.e., the relative flow distance of the suspension, and, accordingly, the fractioning time is determined by the length of the helical channel.
BRIEF SUMMARY OF THE INVENTION
Consequently, the object of the present invention is to provide a fractionator, that enables continuous fractioning and a long fractioning distance.
In a fractionator of the kind initially stated, this is achieved in that the flow channel extends from the inlet forth and back between the end walls of the drum and radially outwards towards outlet means for the at least two fractions. Preferably, the flow channel is defined by substantially concentric cylindrical walls, of which every second in its one axial end is tightly connected to one end wall of the drum and every second in its one axial end is tightly connected to the other end wall of the dru
REFERENCES:
patent: 5524769 (1996-06-01), Spencer
Abstract of JP A 57-53253, vol. 6, No. 127, C-113.
Engewik Terje
Oswaldsson Rolf
Rasmussen Sigmund
Strid Kent
Kvaerner Pulping AS
Nguyen Tuan N.
Terrell William E.
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