METHOD AND APPARATUS FOR CLEANING LIQUIDS, USING LOOSE FILTER MATERIAL, WHICH IS FLUIDIZED DURING BACKWASH

摘要

A method for purification of liquids, particularly water, by filtering the liquid through a filter consisting of a bed of particulate filtering mass (54) in a filter vessel (50), which filter is purged of collected impurities by supplying high-pressure flushing liquid from below through the filtering mass. The invention is characterized in that the filter bed is brought to expand when the flushing liquid is introduced from below during at least one flushing phase, so that the filtering mass is fluidized and the flushing liquid can pass through all parts of the filtering bed and disengage collected impurities from the filtering mass, said impurities being driven upwardly through the filtering bed and collected in the upper part of the vessel, in that the supply of flushing liquid from below is interrupted so that the filtering bed during a sedimentation phase is allowed to settle back to its starting level (55) and resume its normal volume, and in that the liquid volume above the filtering bed containing spent flushing liquid and impurities freed of the filtering bed are drained during a draining phase through a plurality of discharge nozzles (62) located at a level substantially lower than the normal upper level in the vessel but above the upper level of the filtering bed, the upper level of the liquid sinking to the level of the discharge nozzles.