Method and assembly for processing cellulose pulp of wood processing industry

Abstract

A method of and an apparatus for processing cellulose pulp of wood processing industry. The method and assembly may be used, on one hand, as a pressure diffuser for washing the pulp before an oxygen stage and, on the other hand, the separation of soap, gas and/or other light materials from filtrates and from black liquor of a cellulose mill in a pressurized device, as well as the new process connections enabled by the method. The method and apparatus may process filtrates from brown stock washing and bleaching as well as black liquors from a digesting department and an evaporation plant. By way of example, the filtrate of the washing department is pumped to the digesting department of a sulfate cellulose mill as well as the black liquor taken from the digesting department to an evaporation plant.

I claim: 
     
         1 . A method of processing cellulose pulp, which is produced by digesting from softwood or hardwood chips in a digester, the method comprising:
 washing digested pulp;   processing the washed pulp in an oxygen stage, and   after the oxygen stage, washing and bleaching the washed pulp, and   separating in a pressurized separation apparatus soap, gas or other light materials produced in a digesting process from a filtrate or from black liquor generated by a digester.   
     
     
         2 . The method of  claim 1  wherein the pressurized separation apparatus is at least one of a hydrocyclone, a centrifuge and a pump. 
     
     
         3 . The method according to  claim 1 , the filtrate is from the washing of digested pulp and the separation separates the filtrate into a soap fraction and filtrate fraction essentially free of soap. 
     
     
         4 . The method according to  claim 3 , wherein the essentially soap-free filtrate fraction is fed as washing liquid to another washing stage or into a digester. 
     
     
         5 . The method according to  claim 3  wherein the soap fraction is fed directly to an evaporation plant or to black liquor flowing to the evaporation plant. 
     
     
         6 . The method according to  claim 1 , wherein the black liquor obtained from the digester is fed to the pressurized separation apparatus and the black liquor is separated into soap fraction and a black liquor essentially free of soap. 
     
     
         7 . The method according to  claim 1  wherein the washing and bleaching in performed in a bleaching plant includes a suction leg, sub-atmospheric pressure or a press is used in at least one washing stage of the bleaching plant, and a pressure of a filtrate from the at least one washing stage is adjusted by using at least one of a bypass valve in the washer or the press, and an overflow fraction valve of the pressurized separation apparatus, and the filtrate is fed to the pressurized separation apparatus to separate soap from the filtrate. 
     
     
         8 . A method according  claim 1 , in which the separation is performed at a temperature of at least above 100 degrees Celsius. 
     
     
         9 . An assembly for processing cellulose pulp comprising:
 a digester configured to produce pulp by digesting wood chips;   a washer coupled to a discharge of the digester and configured to wash pulp discharged from the digester;   an oxygen reactor coupled to a discharge of the washer and configured to receive pulp from the washer;   a bleaching plant coupled to a discharge of the oxygen reactor and configured to receive pulp form the oxygen reactor, and   a pressurized separation apparatus coupled to a black liquor output of the digester or to a filtrate output of the washer.   
     
     
         10 . The assembly as in  claim 9  wherein the pressurized separation apparatus is one of a hydrocyclone, a centrifuge or a pump. 
     
     
         11 . The assembly according to  claim 9 , in which the pressurized separation apparatus is in a filtrate circulation including the digester and a subsequent washer. 
     
     
         12 . The assembly according to  claim 9  wherein the pressurized separation apparatus is in a black liquor circulation including the digester and an evaporation plant. 
     
     
         13 . The assembly according to  claim 9 , wherein the washer includes a suction leg, and the pressurized separation apparatus receives filtrate from the washer. 
     
     
         14 . A method to process cellulose pulp comprising:
 digesting cellulosic material in a pressurized digesting vessel to produce digested pulp, wherein the pressure in the digesting vessel is greater than atmospheric pressure;   washing the digested pulp in a pressure diffuser, wherein the pressure in the pressure diffuser is greater than the atmospheric pressure;   processing the washed pulp in an oxygen reactor, wherein the pressure in the oxygen diffuser is greater than the atmospheric pressure;   maintaining the washed pulp at a pressure greater than the atmospheric pressure as the washed pulp flows from the pressure diffuser to the oxygen reactor, and   separating in a pressurized separation apparatus soap, gas or other light materials produced in the digesting of the cellulosic material or the washing of the pulp.