Process and configuration for providing external upflow/internal downflow in a continuous digester

Abstract

A continuous digester configuration and process for continuously cooking and digesting cellulosic material and producing cellulosic pulp is disclosed. The digester configuration comprises a plurality of jump-stage recirculations located along the length of a continuous digester vessel, wherein each of the jump-stage recirculations moves extracted liquor from one elevation of the digester vessel and re-introduces the liquor at a higher elevation in the vessel to maintain an internal liquor downflow substantially throughout the entire digester vessel. The process for continuously cooking and digesting cellulosic material comprises maintaining an internal concurrent liquor downflow substantially throughout the continuous digester vessel, wherein the internal liquor downflow does not exceed 400 gallons per ton of b.d. wood feed.

What is claimed is:  
     
         1 . A digester for continuously cooking and digesting cellulosic material and producing cellulosic pulp comprising: 
 a plurality of jump-stage recirculations located along the length of a continuous digester vessel, wherein each of the jump-stage recirculations moves extracted liquor from a first elevation of the digester vessel and re-introduces the extracted liquor into the vessel at a second higher elevation to maintain an internal liquor downflow substantially throughout the entire digester vessel.    
     
     
         2 . The digester of  claim 1 , wherein the internal liquor downflow does not exceed 400 gallons per ton of b.d. wood feed substantially throughout the entire digester vessel.  
     
     
         3 . The digester of  claim 1  further comprising a plurality of liquor extraction and addition points along the length of the digester.  
     
     
         4 . The digester of  claim 3  further comprising a flow-indicator-control system associated with each jump-stage recirculation and liquor extraction and addition points.  
     
     
         5 . The digester of  claim 1 , wherein the digester vessel comprises a plurality of extraction screens along the length of the vessel, each extraction screen having a jump-stage recirculation.  
     
     
         6 . A digester for continuously cooking and digesting cellulosic material and producing cellulosic pulp comprising: 
 a jump-stage recirculation located along the length of a continuous digester vessel, wherein the jump-stage recirculation moves extracted liquor from a first elevation of the digester vessel and re-introduces the liquor into the vessel at a second higher elevation to maintain an internal liquor downflow substantially throughout the entire vessel that does not exceed 400 gallons per ton of b.d. wood feed.    
     
     
         7 . The digester of  claim 6  further comprising a plurality of liquor extraction and addition points along the length of the digester.  
     
     
         8 . The digester of  claim 7  further comprising a flow-indicator-control system associated with the jump-stage recirculation and liquor extraction and addition points.  
     
     
         9 . A process for continuously cooking and digesting cellulosic material and producing cellulosic pulp in a continuous digester comprising: 
 (a) maintaining an internal, con-current liquor downflow substantially throughout a continuous digester vessel, wherein the internal liquor downflow does not exceed 400 gallons per ton of b.d. wood feed.    
     
     
         10 . The process of  claim 9 , wherein the continuous digester vessel comprises a plurality of jump-stage recirculations located along the length of the vessel, and each of the jump-stage recirculations moves extracted liquor from a first elevation of the digester vessel and re-introduces the extracted liquor into the vessel at a second higher elevation to maintain the internal liquor downflow substantially throughout the entire digester vessel.  
     
     
         11 . The process of  claim 9 , wherein the continuous digester vessel comprises a plurality of liquor extraction and addition points along the length of the digester.  
     
     
         12 . The process of  claim 11 , wherein the continuous digester vessel further comprises a flow-indicator-control system associated with each jump-stage recirculation and liquor extraction and addition points.  
     
     
         13 . The digester of  claim 9 , wherein the digester vessel comprises a plurality of extraction screens along the length of the vessel, each extraction screen having a jump-stage recirculation.