Liquid purification or separation – Processes – Separating
Patent
1992-05-21
1995-10-24
Cintins, Ivars
Liquid purification or separation
Processes
Separating
2102423, 210923, E02B 1504
Patent
active
054607353
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an improved method and apparatus for recovering a liquid which is floating on another liquid, for example, oil floating on water, or oil of low specific density floating on oil of higher specific density.
BACKGROUND OF THE INVENTION
It is known to remove oil from water on which it is floating using devices called oleophilic skimmers. These oleophilic skimmers are rotating discs usually provided in sets, mounted on axes parallel to the liquid surface such that each disc is partially immersed in the liquid. As each disc rotates, the surfaces of the immersed portion thereof become coated with oil which is then carried away from the bulk liquid as the disc continues to rotate. The oil is removed from each disc at a point further along the rotation path by a scraper or blade associated with the disc and is then channelled to the oil outlet or tank.
SUMMARY OF THE INVENTION
Examples of oleophilic skimmer apparatus are described in British patents numbers 1419114, 1523590 and 1554458 as well as in published British patent applications 2041231, 20508556 and 2156234.
It has now been found that improved oil recovery rates may be obtained using an oleophilic skimmer apparatus in which at least one disc is provided rotating in a plane which is inclined at an acute angle to the liquid surface.
In particular, it has been found that the uptake of oil by the disc, or discs, increases as the angle between the plane of the disc and the liquid surface decreases. However, at low angles, although the rate of uptake of oil is still high, emulsification of the floating oil begins to occur. That is, at disc inclination angles of about 15.degree. and lower, the shear forces acting on the floating oil globules tend to disrupt the globules and cause an emulsion to form. This impairs the performance of the apparatus.
Accordingly, in order to obtain a good rate of oil recovery, whilst avoiding the problems of emulsification of the floating oil, it would be preferable to angle the oleophilic skimmer disc, or discs, at about 20.degree. to the liquid surface. Furthermore, some tests have shown a peak in recovery rates using discs angled at 20.degree. to the liquid surface.
In practice, there are difficulties in physically collecting the oil taken up by a disc angled at so shallow an angle as 20.degree. to the liquid surface. It has been found to be simpler to collect the oil using a slightly greater angle of disc inclination (25.degree.-30.degree.) and a reasonably high rate of oil uptake has still been achieved. For smaller discs, having a diameter of 280 mm for example, an inclination angle of 25.degree. has been found to provide an optimal compromise between rate of oil uptake and ease of collection. For larger discs, having diameters of 1-2 metres, a somewhat greater angle of 28.degree. provides a better compromise position. For discs of even greater diameter a slightly larger inclination angle than 28.degree. may be necessary, but it is believed that the rate of change of the optimal angle with increasing disc diameter levels off and it is not expected to exceed more than about 30.degree. even for extremely large discs.
Another advantage of using oleophilic discs inclined at an acute angle to the liquid surface (e.g. inclined at about 70.degree. or less to the liquid surface) is that it is possible to collect the oil without impurities if the peripheral speed of the disc is appropriately selected (the required speed varies with the type of oil being collected). In particular, by selecting the correct rotational speed for an inclined disc it becomes possible to collect oil omitting even the impurities which cause a coloured appearance (i.e. the collected oil is colourless).
Furthermore, when using oleophilic skimmer discs inclined at an acute angle to the liquid surface (e.g. inclined at about 70.degree. or less to the liquid surface) an additional advantage is obtained in that the collected liquid is in a purer form. For example, when oil is collected from the surface of a body
REFERENCES:
patent: 4021344 (1977-05-01), Webb
patent: 4051024 (1977-09-01), Lowe et al.
patent: 4368122 (1983-01-01), Ravagnan
patent: 4642185 (1987-02-01), Turner et al.
patent: 4741827 (1988-05-01), Klinar et al.
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