Screen basket having diagonal slots for top separator of a digester

Abstract

A screen basket in a top separator for a cellulosic material treatment vessel, the screen basket includes: a cylindrical plate having a vertical joint connecting opposite edges of the plate, rows of slots extending through the plate, and each slot has a curved or chamfered inlet corner edge adjacent an inside surface of the plate and is oblique to a vertical axis of the basket.

What is claimed: 
     
         1 . A screen basket for top separator for a cellulosic material treatment vessel, the screen basket comprising:
 a cylindrical plate having a vertical joint connecting opposite edges of the plate, and   rows of slots extending through the plate, wherein each slot has a curved or chamfered inlet corner edge adjacent an inside surface of the plate and each slot is oblique to a vertical axis of the basket.   
     
     
         2 . The screen basket of  claim 1  where the curved corner inlet slot edge is at least one of rounded, chamfered, sloped or inclined. 
     
     
         3 . The screen basket of  claim 1  wherein the curved inlet corner edge has a radius of curvature in a range of one third to two thirds a thickness of the plate. 
     
     
         4 . The screen basket of  claim 1  wherein the curved or chamfered corner edge is only at a lower edge of each slot. 
     
     
         5 . The screen basket of  claim 1  wherein the slots are each offset along an axis from the inside surface to an outside surface of the plate by an angle of between 5 degrees to 45 degrees. 
     
     
         6 . The screen basket of  claim 1  wherein the curved or chamfered inlet corner edge is limited to an upper corner edge or a lower corner edge. 
     
     
         7 . The screen basket of  claim 1  wherein the slots are oblique to the vertical axis at an angle of 1 degree to 75 degrees. 
     
     
         8 . The screen basket of  claim 1  wherein the rows of slots uniform in height and orientation of the slots. 
     
     
         9 . The screen basket of  claim 1  wherein the slots in each row are uniform in shape and dimensions, and the dimensions of the slots differ from row to row. 
     
     
         10 . A method for extracting a liquid from a top separator of a treatment vessel, the method comprising:
 feeding a slurry of cellulosic material and a liquid in the top separator screen basket of a vessel, wherein the slurry of cellulosic material and liquid flows into the screen basket;   extracting a portion of the liquid in the slurry of cellulosic material and liquid through a screen basket assembly, wherein the screen basket formed of a screen basket plate within the top separator and is formed around a conveyor screw device, and the screen basket plate includes slots having curved or chamfered inlet corner edges adjacent an inside surface of the screen basket plate and facing a flow of slurry of cellulosic material and liquid, and   deflecting cellulosic material flowing through the top separator with the curved or chamfered inlet corner edges to avoid the material become caught in the slots of the screen basket.   
     
     
         11 . A top separator for use in a treatment vessel comprising:
 a rolled plate formed into a cylindrical screen;   rows of diagonal slots formed in the plate and oriented horizontally;   a single welded joint extending vertically between abutting edges of the plate.   a conveyor screw within interior to the cylindrical screen, wherein a gap between an outer edge of the screw and an interior surface of the cylindrical screen is no greater than ten thousandths of an inch;   a housing supporting the cylindrical screen and forming a liquid chamber between the housing and screen, and   a vertical shaft supporting the screw and extending vertically through the cylindrical screen.   
     
     
         12 . The top separator of  claim 11  where the diagonal slots include a curved corner inlet slot edge that is at least one of rounded, chamfered, sloped and inclined. 
     
     
         13 . The top separator of  claim 12  wherein the curved inlet corner edge has a radius of curvature in a range of one third to two thirds a thickness of the plate. 
     
     
         14 . The top separator of  claim 12  wherein the curved or chamfered corner edge is only at a lower edge of each slot. 
     
     
         15 . The top separator of  claim 11  wherein the slots are each offset along an axis from the inside surface to an outside surface of the plate by an angle of between 5 degrees to 45 degrees. 
     
     
         16 . The top separator of  claim 11  wherein the curved or chamfered inlet corner edge is limited to an upper corner edge or a lower corner edge. 
     
     
         17 . The top separator of  claim 11  wherein the slots are oblique to the vertical axis at an angle of 1 degree to 75 degrees. 
     
     
         18 . The top separator of  claim 11  wherein the rows of slots uniform in height and orientation of the slots. 
     
     
         19 . The screen basket of  claim 11  wherein the slots in each row are uniform in shape and dimensions, and the dimensions of the slots differ from row to row.