Continuous digester having a sectioned top separator with multiple liquor extraction ports

Abstract

A method is disclosed for extracting liquor from a cellulose slurry for a continuous digester comprising the steps of: providing the cellulose slurry of liquor and chips of cellulose fiber material to a separator; extracting a first stream of liquor from the separator; extracting a second stream of liquor from the separator, where the second stream has an effective alkali (EA) concentration greater than the EA concentration of the first steam; outputting the first stream from the separator and outputting the second stream from the separator separately from the second stream, and outputting a condensed slurry from the separator to a digester vessel.

What is claimed is:  
     
         1 . A method for extracting liquor from a cellulose slurry of a continuous digester comprising of: 
 providing the cellulose slurry of liquor and chips of cellulose fiber material to a separator;    extracting a first stream of liquor from the separator;    extracting a second stream of liquor from the separator, where the second stream has an effective alkali (EA) concentration greater than the EA concentration of the first steam;    outputting the first stream from the separator and outputting the second stream from the separator separately from the second stream; and    outputting a condensed slurry from the separator to a digester vessel.    
     
     
         2 . A method for extracting liquor as in  claim 1  wherein the separator is external to the digester vessel.  
     
     
         3 . A method for extracting as in  claim 1  wherein the separator is internal to the digester vessel.  
     
     
         4 . A method for extracting liquor as in  claim 1  wherein the output of the first steam flows to a spent liquor recovery system.  
     
     
         5 . A method for extracting liquor as in  claim 1  wherein the output of the second steam flows to a chip feed system to be added to the slurry upstream of the separator.  
     
     
         6 . A method for extracting liquor as in  claim 1  wherein the output of the second steam flows to a high pressure feeder in a chip feed system to be added to the slurry upstream of the separator.  
     
     
         7 . A method for extracting liquor as in  claim 1  wherein the output of the second steam flows to an inlet to the separator and is added to the slurry flowing into the separator.  
     
     
         8 . A method for extracting liquor as in  claim 1  wherein the output of the second steam is mixed with white liquor to form a liquor mixture that flows to an inlet to the separator and is added to the slurry flowing into the separator.  
     
     
         9 . A method for extracting liquor as in  claim 8  wherein the mixture is heated before flowing to the inlet to the separator.  
     
     
         10 . A method for extracting liquor as in  claim 1  wherein the separator includes a screw conveyor, a screen cylinder, and a first chamber and a second chamber each adjacent to the screen cylinder, wherein the first stream is extracted from the first chamber and the second stream is extracted from the second chamber.  
     
     
         11 . A method for extracting liquor as in  claim 10  wherein the first chamber is upstream along the screw conveyor to the second chamber.  
     
     
         12 . A method for extracting liquor as in  claim 1  wherein the first stream is combined with additional liquor having a high EA concentration, and the combine stream flows to the slurry inlet of the top separator.  
     
     
         13 . A method for extracting liquor as in  claim 1  wherein the second stream has an EA at least 5 gr (As Na OH) EA/1 greater than the EA concentration of the first stream.  
     
     
         14 . A separator for a continuous digester in a cellulose fiber processing system comprising: 
 an inlet receiving a flow of a fiber chip and liquor slurry;    a screw conveyor having a first screw portion near the inlet, and a second screw portion near a slurry outlet to the conveyor, wherein the first and second screw portions are coaxial;    said slurry outlet providing a condensed slurry to a digester vessel;    a cylindrical screen around the screw conveyor, wherein the screen is porous to allow passage of liquor and block fiber chips;    a first liquor chamber adjacent the first screw portion and on a side of the screen opposite to the conveyor;    a second liquor chamber adjacent the second screw portion and on a side of the screen opposite to the conveyor;    a first liquor stream outlet coupled to the first liquor chamber; and    a second liquor stream outlet coupled to the second liquor chamber.    
     
     
         15 . A separator as in  claim 14  wherein the separator is external to the digester vessel.  
     
     
         16 . A separator as in  claim 14  wherein the separator is internal to the digester vessel.  
     
     
         17 . A separator as in  claim 14  wherein the first liquor stream outlet is coupled to a spent liquor recovery system.  
     
     
         18 . A separator as in  claim 14  wherein the second liquor stream outlet is coupled to a chip feed system to be added to the slurry upstream of the separator.  
     
     
         19 . A separator as in  claim 14  wherein the second liquor stream outlet is coupled to a high pressure feeder in a chip feed system to be added to the slurry upstream of the separator.  
     
     
         20 . A separator as in  claim 14  wherein the second liquor stream outlet is coupled to an inlet to the separator.  
     
     
         21 . A separator as in  claim 14  wherein the second liquor stream outlet is a coupled to a source of white liquor and to the inlet to the separator.  
     
     
         22 . A separator as in  claim 14  wherein the second liquor stream, outlet is coupled to a chip feed system to be added to the slurry upstream of the separator.  
     
     
         23 . A separator as in  claim 14  further comprising a divider separating the first chamber from the second chamber.  
     
     
         24 . A separator for a continuous digester in a cellulose fiber processing system comprising: 
 an inlet receiving a flow of a fiber chip and liquor slurry;    a screw conveyor having a slurry flow path along a screw axis, including a first screw portion near the inlet, and a second screw portion near a slurry outlet to the conveyor;    said slurry outlet being downstream of the slurry flow path and providing a condensed slurry to a digester vessel;    a cylindrical screen coaxial to the conveyor and arranged along the flow path, wherein the screen is porous to allow passage of liquor and block fiber chips;    a first annular liquor chamber adjacent the first screw portion and having the screen forming an inner wall to the chamber;    a second liquor chamber adjacent the second screw portion and having the screen forming an inner wall to the chamber;    a first liquor stream outlet coupled to the first liquor chamber; and    a second liquor stream outlet coupled to the second liquor chamber.    
     
     
         25 . A separator as in  claim 24  further comprising an annular disk separating the first chamber from the second chamber.