Method and system for thin chip digester cooking

Abstract

An apparatus to pulp thin wood chips including: a chip screen receiving chips of comminuted cellulosic material, the screen assembly including a screening assembly which outputs thin chips; a chip bin and conveyor assembly receiving the thin chips output from the chip screen, the lower portion of the chip bin is flooded with white liquor; a continuous digester vessel having an chip inlet at an upper region of the vessel coupled to the chip bin and conveyor assembly, a cooking zone extending vertically from the upper region of the vessel to a wash zone which extends from the cooking zone to a bottom region of the vessel, and a pulp discharge outlet in the bottom region; a steam inlet at the upper region of the inlet, an upper region of the digester vessel at an elevated cooking temperature, and a screen assembly near the wash liquid inlet for the wash zone.

What is claimed is: 
     
         1 . An apparatus to pulp thin wood chips comprising:
 a chip screen receiving chips of comminuted cellulosic material, the screen assembly including a screening assembly configured to pass thin chips wherein at least 85% of the chips passing through the chip screen have a thickness between 6 mm and 2 mm;   a chip bin and conveyor assembly coupled to a thin chips output of the chip screen, the chip bin assembly including a chip bin having a white liquor inlet coupled to a source of white liquor and said chip bin having an operating mode in which a lower portion of the chip bin is flooded with white liquor while thin chips move through the chip bin to a discharge outlet of the chip bin, and the chip bin and conveyor assembly including a conveyor having an inlet configured to receive the thin chips from the discharge outlet and an outlet configured to transfer the thin chips to a transport conduit;   a continuous digester vessel including an chip inlet at an upper region of the vessel and coupled to the transport conduit, a cooking zone extending vertically from the upper region of the vessel to a wash zone, the wash zone extending from the cooking zone to a bottom region of the vessel, and a pulp discharge outlet in the bottom region, wherein the continuous digester includes an inlet at the upper region and coupled to a source of steam or other heated fluid to heat the chips in the vessel to at least 130 degrees Celsius, and the continuous digester includes a wash inlet coupled to a source of wash liquid and the continuous digester vessel includes a screen assembly above the wash inlet and the screen assembly includes a screen adjacent a wash filtrate chamber on a side of the screen opposite to a side of the screen assembly adjacent the chips in the wash zone.   
     
     
         2 . The apparatus of  claim 1  wherein the cooking zone in the digester vessel operates at a temperature of at least at least 130 degrees Celsius. 
     
     
         3 . The apparatus of  claim 1  wherein the cooking zone is devoid of screens to extract liquor from the cooking zone. 
     
     
         4 . The apparatus of  claim 1  wherein the cooking zone is devoid of inlets to receive liquor. 
     
     
         5 . The apparatus of  claim 1  further comprising a high pressure transfer device between the chip bin and the chip inlet, wherein the high pressure transfer device increases a pressure of the thin chips. 
     
     
         6 . The apparatus of  claim 1  further comprising an inlet for dilution liquid in the bottom region of the digester vessel. 
     
     
         7 . The apparatus of  claim 6  wherein the inlet for dilution liquid includes a first nozzle directing the dilution liquid in a generally vertical direction into the bottom region and a second nozzle direction the dilution liquid in a generally horizontal direction. 
     
     
         8 . The apparatus of  claim 1  further comprising a liquor filter receiving wash filtrate from the wash filtrate chamber and having a liquor outlet providing liquor to a chip discharge port of the chip conveyor. 
     
     
         9 . The apparatus of  claim 1  wherein the chip bin includes a steam inlet. 
     
     
         10 . The apparatus of  claim 1  wherein the digester vessel is a substantially vertically oriented vessel having a height of at least 30 meters.