Liquid purification or separation – Processes – Separating
Patent
1993-04-06
1995-03-28
Drodge, Joseph W.
Liquid purification or separation
Processes
Separating
209 1, 209155, 209208, 210805, B01D 3704
Patent
active
054014220
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a separation method for solid constituents having different sizes contained in a suspension as well as a filtration device for carrying out this method. The method and device according to the present invention can also be used to wash such suspensions.
Up to now, a technique commonly used to separate solid constituents contained in a suspension consists in using a rotating filter wherein the solution to be filtered is introduced; the filter is rotated so that, due to centrifugal forces acting on the particles, the ones having a size less than the filter pores diameter pass through the rotating filter. The particles which pass through the filter are then recovered in a stationary housing surrounding said rotating filter. Thus, U.K. Patent 2 178 332 discloses a rotating filtering cylinder allowing to filter a determined amount of sand. This patent provides a device allowing to spray a washing fluid on the surface of the rotating cylinder, allowing to clean the filter after having used said filter a number of times. In fact, these devices exhibit drawbacks because they generate a quite rapid clogging of the filtering surface.
In the 70's, the cross flow filtration concept appeared. The principle consisted in directing the suspension parallel to the filter. This technique allowed to increase the filtration rate by minimizing the thickness of the polarizing layers near the filtration surface, depending on the pressure difference between the inner portion of the filtration surface and the outer portion of said surface. However, this technology exhibited the drawback to provide a filtration flow rate decreasing with time, due to the same clogging problem of the filtering surface.
In order to solve this problem, it was suggested to drive the filtering surface into rotation in order to remove the clogging problems and to allow an increase of the filtration flow rate of such filtration devices, the centrifugal forces, as a result of the filter rotation, thus preventing in fact the particles of greater size than the pores size of the filtering surface to deposit. Such devices allowed, with respect to the stationary devices, to multiply the filtration flow rate by six.
However, such devices do not allow a selective separation of particles having different sizes, as would be desired in presence of a suspension including a plurality of particles populations exhibiting different sizes, in order to be able, for example, to isolate such or such type of particles. Up to now, such operations require in fact to change the filtration surface, which is often complex and penalizing as regards to an economical point of view.
By way of example, such a device is disclosed in the French Patent 1 207 441; according to this patent, the filtration device includes a stationary tight housing in which the fluid to be filtered is introduced and an inner rotating filtering surface, the whole filtering device being continuously or intermittently rotated and comprising a pleated, undulated or embossed filtering medium, in order to increase the filtering surface.
Thus, it is an object of the present invention to provide a filtration device of the cleaning by centrifuging type, the filter cutting threshold of which can be modified without changing the filtration surface.
It is another object of the present invention to provide an uncloggable filtration device.
It is still another object of the present invention to be able, for a suspension exhibiting a determined granulometric distribution curve, to isolate a particular range of particles sizes located elsewhere in the distribution curve.
It is still another object of the present invention to provide a device designed to wash suspensions such as photographic emulsions.
It is yet another object of the present invention to provide a device allowing, in a suspension such as a photographic emulsion, to separate particles according to their shape.
Other objects of the present invention will appear during the following detailed disclosure.
The objects of the present invention
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Drodge Joseph W.
Eastman Kodak Company
Ruoff Carl F.
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