Diffuser assembly

In an elongated upright hollow vessel which includes side and bottom walls, the improvement comprising:

• a plurality of withdrawal screens extending substantially parallel to the vessel direction of elongation, and spaced from each other in directions perpendicular to the vessel direction of elongation;
• non-rotatable conduit means for supporting said withdrawal screens and for providing for passage of fluid from said withdrawal screens to an area remote from said withdrawal screens and exterior of said vessel;
• means for only reciprocating said conduit means with attach withdrawal screens up and down in a direction substantially coincident with the direction of elongation of the vessel;
• and means for introducing fluent material to be treated into said vessel and withdrawing treated fluent material therefrom;
• and
• said means for only reciprocating consisting essentially of a linear actuator located below the bottom wall of said vessel within the cross-sectional area of the vessel, for avoiding boiling problems as a result of liquor suck-up during start-up;
• and wherein said conduit means for providing passage of fluid from said withdrawal screens includes a central conduit substantially concentric with said linear actuator and reciprocal with said linear actuator, said central conduit operatively passing through the bottom wall of said vessel.