Abstract: A downflow evaporator for concentrating a descending stream of liquid containing solids comprises a bundle of downflow tubes having open upper ends affixed to an upper tube sheet and open lower ends affixed to a lower tube sheet, the tubes receiving the stream of liquid through the upper ends and discharging it through the lower ends. The liquid is caused to cascade over the entire surface of the upper tube sheet whereby the liquid is distributed thereover and over the open upper tube ends. A covering is placed over the upper end of each downflow tube and spaced therefrom so as to prevent the liquid from dripping into the central portion of the tube whereby the stream of liquid descends peripherally along the inner surface of the tube.

Abstract: Apparatus for countercurrently contacting solids with a liquid comprises a rotatable drum housing a screw conveyor having helical turns affixed to the cylindrical side wall of the drum and defining a helical passageway for the solids between the turns, the passageway is divided into a series of compartments. Each compartment has a grating receiving the solids and raising the received solids while liquid is drained through the grating and then permitting the drained solids to fall into a succeeding compartment, and an imperforate partition trailing the grating in the direction of rotation of the drum, the partition defining a chamber receiving the liquid drained from the solids with the adjacent side wall of the drum and the helical screw turns. A passageway interconnects each chamber with the upstream compartment and these passageways extend along the side wall of the drum.