Imperforate bowl: centrifugal separators – Rotatable bowl – Including structure located within bowl and defining...
Patent
1997-11-24
1999-08-10
Walker, W. L.
Imperforate bowl: centrifugal separators
Rotatable bowl
Including structure located within bowl and defining...
494 77, B04B 104
Patent
active
059350539
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a fractionator for fractioning a suspension in at least two fractions, including a drum rotatable about a substantially horizontal shaft and having an inlet for suspension and at least one outlet for fractions, said drum including at least two walls curved about the shaft and extending substantially parallel thereto in the longitudinal direction thereof, said walls defining between them a fluid channel substantially parallel to the shaft.
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 fibres. However, it is unavoidable that also long fibres accompany the filtrate, which, thus, will contain long fibres, fines, fillers and printing ink. It is, of course, desirable to be able to recover not only the valuable long fibres, 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 largest 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.
In a not pre-published solution (SE-9303193-8) of the problems associated with this known fractionator, a fractionator is suggested including a drum rotatable about a substantially horizontal axis and having axially spaced end walls. From an inlet centrally located in one end wall of the drum, a flow channel extends forth and back between the end walls and radially outwards towards outlet means for the at least two fractions in the other end of the drum. The flow channel is defined by substantially concentric cylindrical walls, of which every second in its one axial end is tightly conn
REFERENCES:
patent: 1057613 (1913-04-01), Baldwin
patent: 2209577 (1940-07-01), Podbielniak
patent: 3791575 (1974-02-01), Lartinen et al.
patent: 4210276 (1980-07-01), Lapshev et al.
Oswaldson Rolf
Strid Kent
Cecil Terry K.
Kvaerner Pulping AS
Walker W. L.
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