Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1995-02-14
1997-12-16
Nessler, Cynthia L.
Liquid purification or separation
Processes
Ion exchange or selective sorption
210676, 210677, 210268, 210269, 210792, 210189, 210807, B01D 2428
Patent
active
056981066
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of filtering a suspension or emulsion, and also relates to a filtering apparatus for carrying out the method.
BACKGROUND OF THE INVENTION
It may be read from the Swedish patent specification 396 552 that filtering a suspension or emulsion in a filter bed comprising particulate filter material may be carried out by allowing the suspension to flow upwards through the filter bed, simultaneously as the filter medium flows downwards through a filtering tank in which the filtration takes place. Filtering thus takes place during counter flow between suspension and filter medium. The suspension is supplied at a lower part of the filter bed and the filtered liquid phase is taken away from a zone above the filter bed. The polluted filter medium close to the bottom of the filter tank is taken out and conveyed to a washing apparatus above the filter bed, and after washing it is returned to the upper side of the filter bed. By continuous supply of suspension to the filter bed, continuous extraction of filtered liquid phase as well as continuous conveyance of polluted filter medium to the washing apparatus and washed filter medium back to the filter bed results in that the filtering apparatus operates completely continuously, and does not normally need to be taken out of operation.
Such filtering apparatus may reach considerable dimensions in order to receive large suspension flows. In large installations there may be a plurality of filtering units, which are placed side by side and work in parallel, this being more practical or more suited to the available space. A method of arranging a large installation of this kind is illustrated in FIG. 3 of the previously mentioned patent specification 396 552. A normal circular shape of the filtering units has been departed from here, and a hexagonal shape has been adopted to achieve compaction of the units. Since conveyance of the filter medium to the washing apparatus takes place through the filter bed, and the washing apparatus is also within the outer shell of the unit, there is nothing to prevent such compaction of such filtering units.
A number of factors affect the selection of the filter apparatus size, such as type of suspension or emulsion, desired purification degree, type of filter medium and, as previously mentioned, the magnitude of the suspension flow that is to be filtered. These factors determine the area and height of the filter bed body or bodies. The filtering apparatus is then designed from these dimensions, e.g. as is illustrated in FIG. 1 of the mentioned patent specification 396 552.
Although this figure is only a principle sketch, the proportions of the figure do not differ from reality to any notable degree. Accordingly, the observation may be made that a considerable portion of the height of the filtering apparatus has been used to make room for the polluted filter medium washing apparatus. In the case where the available height is limited in the space where the filter units are to be placed, the height of these tanks will cause some limitations in the design.
SUMMARY OF THE INVENTION
The present invention has come about to provide a filter, which has a considerably lower construction height for a given and unchanged volume of the filter medium. In accordance with the invention this has been arranged by sinking the lower part of the washing apparatus to a level under the upper surface of the filter bed, but with retention of a characteristic method of carrying out washing. This method of washing involves the provision of an upward current of washing liquid, constituting the ready-filtered liquid phase, in a washing path where the polluted filter medium is caused to fall downwards against the washing liquid flow. Since the washed filter medium comes in at a level which is too low in relation to the filter bed, due to sinking the level of the washing apparatus, extra conveying equipment for the filter medium up to the upper side of the filter bed will be required.
BRIEF DESCRIPTION
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Hakansson Sven
Hjelmner Ulf
Larsson Hans
Nessler Cynthia L.
Nordic Water Products AB
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