A liq.-solid extn. appts. of the rotary drum type incorporates elements of two spiral conveyors and liq. ducts by means of which two fractions of solid materials and two flows of liq. are made to progress countercurrently and separately. During a rotation of 360 degrees of the drum each fraction of solid material undergoes an axial displacement equal to a half pitch of the spiral conveyor, partly in mixt. with the liq. and partly out of the liq. while sliding on a diametral partition after sepn. of the liq. and solid, and each liq. fraction undergoes an axial displacement of one pitch of the spiral conveyor. An existing appts. incorporates a rotary drum, two spiral conveyors, a solid partition creating with the solid radial walls of the screw conveyors two series of consecutive cells and a perforated basket in each cell to separate the solid materials from the liq. Ducts of radial section ensure the displacement of the liq. collected between the baskets and the partition and induce a flow of this liq. in a direction parallel to the axis of the drum. The new appts. incorporates, associated with each of the liq. ducts extending in the direction of the axis of the drum, a liquid duct in each cell extending transversely to the axis, near to it, to recover the liq. sepd. from the solid materials and flowing over the partition when the latter occupies a position near the horizontal and has passed beyond this position. The associated ducts open in the same cell and empty into the same cell. The modification improves the conditions of the liq.-solid sepn. phase and extends the duration of this phase. It prevents a part of the liq. sepd. at the end of the rising of the solid materials from accompanying them during their sliding on the diametral partition. construction is simplified, cost is reduced, maintenance is easier and the basket surface can be distributed more efficiently.
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