Vacuum washer drum
A vacuum drum washer is designed to enable the use of an end-draining drum for drum lengths exceeding 20 feet. The drum washer includes a cylindrical drum having a mesh screen defining an exterior wall. A plurality of outer filtrate channels are disposed radially inward from the mesh screen. A plurality of inner filtrate channels are disposed radially inward from the outer filtrate channels and extend along generally less than an entire length of the drum. A transfer channel connects the outer filtrate channels and the inner filtrate channels. A plurality of radial drainage chutes are disposed adjacent a head end of the outer and inner filtrate channels, which direct the filtrate to a drain valve.
1. A method of washing pulp for the manufacture of paper, the method comprising:
rotating a cylindrical drum having a mesh screen defining an exterior wall in a vat of pulp;
applying a vacuum within the cylindrical drum until a pulp mat is deposited on the exterior wall;
applying a washing liquid to the pulp mat on the exterior wall, the washing liquid flowing as filtrate through the pulp mat and through the mesh screen into a plurality of outer filtrate channels disposed radially inward from the mesh screen;
diverting at least a portion of the filtrate into a plurality of inner filtrate channels disposed radially inward from the outer filtrate channels via a transfer channel connecting the outer filtrate channels and the inner filtrate channels; and
directing the filtrate to a drain valve via a plurality of radial drainage chutes disposed adjacent a head end of the outer and inner filtrate channels.
2. A method according to claim 1 , wherein a downstream end of the transfer channel is disposed in fluid communication with a start of the inner filtrate channels, and wherein the diverting step is practiced by diverting the portion of the filtrate from the outer filtrate channels to the start of the inner filtrate channels.