Liquid purification or separation – Particulate material type separator – e.g. – ion exchange or... – Gravity flow of particles type
Patent
1981-10-26
1983-08-16
Cintins, Ivars C.
Liquid purification or separation
Particulate material type separator, e.g., ion exchange or...
Gravity flow of particles type
B01D 2312
Patent
active
043990347
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an apparatus for filtering a liquid through a movable filter bed consisting of granular material, which is scavenged continuously.
A filtering technique in this connection implies that a liquid containing dissolved and solid impurities is passed through a bed of granular material, usually sand, whereby material suspended in the liquid is separated and remains in the bed. By special inserts also substances dissolved in the liquid can be flocculated out prior to or in the filter and thereafter be separated therein.
Filtering normally takes place in a stationary bed with vertically directed flow and, owing to the separation of impurities, with ever increasing filter resistance. After a certain time the filtering operation is interrupted, and the bed is scavenged with liquid, in certain cases with liquid and air.
During the scavenging process relatively large amounts of water are consumed, which are recovered for being cleaned. The scavenging process further requires special installations in the form of pumps, valves, pipes, automatic equipment etc., to an extent which in relation to the installations required for filtering is considerable.
In order to avoid interruption for scavenging and to reduce the extent of the scavenging equipment, a known technique has been developed which applies a movable filter bed, the material of which is scavenged continuously and successively, and at which the scavenged material is returned to the movable bed. The polluted filter material is removed from the lower portion of the bed together with liquid and is transported by pumping to a washing plant, from which cleaned bed material is returned to the bed, and dirty scavenging liquid is directed away to be cleaned.
In a known apparatus the filtering takes place with downward flow, in the case of a circular bed with radial flow, in the bed to a vertical outlet screen in direct contact with the filter material. The transport of polluted filter material from the lower bed portion takes place with filtered liquid directly from the filter bed. The washing of the material is carried out with transport liquid and incoming unfiltered liquid. Due to the movements of the bed, this method implies that the filter material closest to the outlet screen can contain impurities to such an amount, that the possibility of a certain discharge thereof together with outgoing liquid cannot be excluded. The openings in the outlet screen which in view of the gain size of the filter material are small, also are subject to the risk of clogging.
In another known apparatus the filtering takes place with upward vertical flow in the bed to a liquid volume located above the bed surface, from which volume cleaned liquid is drained through grooves in the liquid surface. The transport of polluted filter material is carried out in the same way as in the apparatus described above, but the washing of the material in this case is carried out with transport liquid and outgoing filtered liquid. The washed bed material is returned to the bed through the filtered liquid volume above the bed surface. This implies the possibility that dirt is transferred to the outgoing liquid when the material washing is not satisfactory.
The two methods described have in common, that the liquid required for material transport is drained from the system after having being used only once and together with added liquid. The applicability of these apparatus, therefore, is restricted for the reasons as follows.
The transport of granular material in a liquid presupposes a flow rate in the liquid which is adjusted to the material. When a transport liquid is being used once, it is essential that its amount can be maintained in a reasonable proportion in relation to the filtered liquid amount. It is further essential to state that the size of coarser impurities, which can be supplied to a filter, not only depends on the design of the infeed devices but also on the dimension of the pipes, in which the impurities after separation are to be transported.
The present inventi
REFERENCES:
patent: 2057887 (1936-10-01), Elliott et al.
patent: 3575294 (1971-04-01), Hirowatari et al.
patent: 3598235 (1971-08-01), Demeter
patent: 4000066 (1976-12-01), Squires
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