Removal of water-soluble compounds from wood chips prior to cooking

Abstract

Processes and systems for the treatment of wood chips prior to cooking remove substantially (e.g., at least about 30%) water-soluble compounds therein, especially those compounds which disassociate in water to form potassium and/or chloride ions and/or water-soluble metal compounds such as manganese, calcium and potassium. In preferred embodiments, wood chips entering the cooking system containing water-soluble compounds, such as those compounds which disassociate in water to form potassium and/or chloride ions and/or water-soluble metal compounds such as manganese, calcium and potassium, may be treated prior to cooking by being brought into contact with an aqueous treatment stream (e.g., water or steam condensate) at a temperature (e.g., between about 20° C. to about 120° C.) and for a time (e.g., between about 2 to 200 minutes) so as to reduce substantially (e.g., at least about 30%) such water-soluble compounds.

What is claimed is:  
     
         1 . A process for treating wood chips prior to cooking in a digester, comprising bringing wood chips into contact with an aqueous treatment stream at a temperature and at a time to reduce substantially water-soluble compounds therein.  
     
     
         2 . The process of  claim 1 , wherein the water-soluble compounds comprise potassium-containing and/or chloride-containing compounds  
     
     
         3 . The process of  claim 1 , wherein the water-soluble compounds include potassium-containing compounds which are reduced by at least about 30%.  
     
     
         4 . The process of  claim 1 , wherein prior to bringing the wood chips into contact with the aqueous treatment stream, there is practiced the step of contacting the wood chips with steam.  
     
     
         5 . The process of  claim 1 , wherein said step of bringing the wood chips into contact with the aqueous treatment stream in a sequential series of wash vessels.  
     
     
         6 . The process of  claim 1 , wherein said temperature is between about 20° C. to about 120° C.  
     
     
         7 . The process of  claim 1 , wherein said temperature is between about 30° C. to about 90° C.  
     
     
         8 . The process of  claim 1 , wherein said time is between about 2 to about 200 minutes.  
     
     
         9 . The process of  claim 1 , wherein said water soluble compounds are reduced by an amount of at least 30 wt. %.  
     
     
         10 . The process of  claim 9 , wherein said water soluble compounds are reduced by an amount of at least about 50 wt. %.  
     
     
         11 . The process of  claim 9 , wherein said water soluble compounds are reduced by an amount of at least about 70 wt. %.  
     
     
         12 . The process of  claim 1 , wherein said aqueous treatment stream is at a pH of between about 2 to about 12.  
     
     
         13 . The process of  claim 1 , wherein said aqueous treatment stream is at a pH of between about 4 to about 10.  
     
     
         14 . The process of  claim 1 , wherein said water soluble compounds include at least one selected from the group consisting of potassium compounds and chloride compounds.  
     
     
         15 . The process of  claim 1 , wherein said water soluble compounds include at least one water-soluble metal selected from the group consisting of manganese, calcium and potassium.  
     
     
         16 . The process of  claim 1 , wherein the aqueous treatment stream includes a wash liquid which is at least one selected from the group consisting of hot water, bleach plant filtrates, collected rain water, evaporator condensate and other mill condensates.  
     
     
         17 . The process of  claim 1 , wherein said step of bringing wood chips into contact with an aqueous treatment stream is conducted at an elevated pressure condition.  
     
     
         18 . The process of  claim 17 , wherein said elevated pressure condition does not exceed a pressure of the digester.  
     
     
         19 . A system for treating wood chips prior to cooking in a continuous digester comprising: 
 a chip bin for containing wood chips to be treated,    at least one wash vessel downstream of the chip bin for receiving steamed wood chips therefrom; and    a treatment line for introducing an aqueous treatment stream into the at least one wash vessel to thereby bring said aqueous treatment stream into contact with the wood chips therein at a temperature and at a time to reduce substantially water-soluble compounds therein.    
     
     
         20 . The system of  claim 19 , comprising a series of wash vessels, wherein said aqueous treatment stream is introduced into each of said wash vessels.  
     
     
         21 . The system of  claim 20 , further comprising a retention vessel between two of said wash vessels in said series.  
     
     
         22 . The system of  claim 21 , wherein said retention vessel is positioned between initial and intermediate ones of said vessels.  
     
     
         23 . The system of any one of claims  19 - 22 , wherein said aqueous treatment stream is introduced in countercurrent flow relative to the flow of wood chips.  
     
     
         24 . The system of  claim 20 , wherein said vessels include a drain line to drain liquid therefrom.  
     
     
         25 . The system of  claim 24 , wherein said drain line includes one line for directing a portion of drained liquid to a wastewater treatment system, and another line for directing another portion of drained liquid to an upstream one of the wash vessels.  
     
     
         26 . The system of  claim 19 , wherein the chip bin includes a meter screw.  
     
     
         27 . The system of  claim 19 , comprising a steam line for injecting steam into the wood chips contained within the chip bin.  
     
     
         28 . The process of  claim 19 , wherein said temperature is between about 20° C. to about 120° C.  
     
     
         29 . The process of  claim 19 , wherein said temperature is between about 30° C. to about 90° C.  
     
     
         30 . The process of  claim 19 , wherein said time is between about 2 to about 200 minutes.  
     
     
         31 . The process of  claim 19 , wherein said aqueous treatment stream is at a pH of between about 2 to about 12.  
     
     
         32 . The process of  claim 19 , wherein said aqueous treatment stream is at a pH of between about 4 to about 10.