Liquid purification or separation – Processes – Separating
Patent
1993-04-07
1995-01-17
Dawson, Robert A.
Liquid purification or separation
Processes
Separating
210797, 210808, 210117, 2103601, 210406, 2104161, 209198, 209350, 209502, 209906, B01D 3306, B01D 3356, B01D 3382
Patent
active
053823702
DESCRIPTION:
BRIEF SUMMARY
In our PCT International Publication WO 91/01815 there is described an arrangement whereby a suspension of solid particulate material in a liquid is passed through a screen or sieve in order to separate the coarse particles from finer particles within the suspension.
It has been found, that although the screening operation according to that invention is effective, commercial requirements demand a higher throughput of the particulate material.
By experiment it has now been found that a faster screening rate can be achieved if there is provided a differential between atmospheric pressure above and below the screen. Thus, when the atmospheric pressure beneath the screen is lower than that above the screen it is found that the particles in suspension pass more rapidly through the screen.
In accordance with the invention there is provided a process for continuously separating relatively coarse particles from a suspension of a mixture of particles in a liquid wherein the suspension is caused to pass through a screening medium which is rotating in its own plane so that the coarse particles are retained on the surface of the screening medium and wherein the atmospheric pressure above the screening medium is caused to be in excess of the pressure below that medium.
A pressurized gas may be applied above the screening medium, and may be compressed air.
Alternatively a partial vacuum may be created beneath the screening medium, and this may be created within the confines of a drum located below the level of the screening medium.
When the drum is formed at its lower portion with plurality of holes for the emission of the finer particles in suspension after screening, the partial vacuum may be formed by passing air out through those holes, for example by means of a connection to a vacuum source.
The partial vacuum may be created by means of a plurality of outwardly projecting members provided on the drum adjacent the holes, whereby rotation of the drum creates a venturi effect over the outer face of the members thereby sucking out the air through the holes.
The differential [.DELTA.P] between the pressures above and below the screening medium may be controlled to be within a pre-determined range by introducing air at atmospheric pressure into the area below the screening medium when the differential pressure [.DELTA.P] exceeds a maximum of the pre-determined range.
The air at atmospheric pressure may be caused to enter the area below the screening medium via a valve which is automatically actuated in response to a variation in the differential pressure [.DELTA.P] which causes .DELTA.P to rise above the maximum of the pre-determined range.
The invention further comprises apparatus for continuously separating relatively coarse particles from a suspension of a mixture of particles in a liquid wherein the suspension is caused to pass through a screening medium which is rotating in its own plane so that the coarse particles are retained on the surface of the screening medium, and wherein the atmospheric pressure above the screening medium is caused to be in excess of the pressure below that medium.
Means may be provided to apply a pressurized gas above the screening medium and the pressurized gas may be compressed air.
Alternatively, means may be provided to cause the pressure beneath the screening medium to be diminished and so cause a partial vacuum to exist thereunder.
Preferably the partial vacuum is created within the confines of a drum located below the level of the screening medium.
The drum may be provided with side walls which are formed with a plurality of holes through which the finer particles in suspension are caused to be emitted, and where means are provided to create a partial vacuum within the confines of the drum by passing air out through those holes.
There may be provided a connection to a vacuum source in order to suck out the air from within the confines of the drum.
A plurality of outwardly projecting members may be provided on the drum adjacent the holes whereby rotation of the drum creates a venturi
REFERENCES:
patent: 3547267 (1970-12-01), Sutherland
patent: 4613432 (1986-09-01), Racine et al.
patent: 4718945 (1988-01-01), Schaper et al.
patent: 4936990 (1990-06-01), Brunsell et al.
Packaging Applications of Polytetrafluoroethylene, Packaging, Mar. 1969, pp. 80-83.
Falcon-Steward Hugh R.
Jones Thomas R.
Phillips Reginald L.
Dawson Robert A.
ECC International Ltd.
Walker W. L.
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