Continuous sawdust cooking process for producing pulp, involves adding filtrate from washing step and white liquor to basing vessel to form part of cooking liquid

摘要

The filtrate (TF) from the washing step and white liquor (WL) are added to the basing vessel (2) to form part of the cooking liquid. The consistency of the cooking liquid/sawdust mixture is kept below a given level. A continuous cooking process for producing pulp from wood in the form of sawdust comprises the following steps : (a) addition of sawdust to the top of a basing vessel ; (b) basing and heating of the sawdust in the vessel using steam (LPST) ; (c) impregnation with cooking liquid in the bottom of the vessel ; (d) pumping the sawdust/cooking liquid mixture from the bottom of the basing vessel into the top of a cooking vessel (5), establishing a sawdust level (CL2) which lies above the cooking liquid level (LL2) ; (e) supplying steam (MPST) to the vessel so that sawdust above the cooking liquid level is heated to the full cooking temperature of 130-160 deg.C ; (f) cooking the sawdust for 60-300 minutes ; (g) supplying the cooking vessel contents to a pressurised diffusion washer (7), in which the cooking liquid is separated from the sawdust and forms a filtrate ; (h) addition of the filtrate to the basing vessel to form part of the cooking liquid so that the filtrate forms more than 50 % of the total amount of cooking liquid ; (i) addition of white liquor to the impregnation vessel and optionally during pumping into the cooking vessel so that it forms part of the cooking liquid ; and (j) maintaining a consistency of no more than 20 (15-17) % for the cooking liquid/sawdust mixture.