A method, uses of the same, a pulp composition, and a system

Abstract

According to an example aspect of the present invention, there is provided a method comprising: providing a pulp composition; screening the pulp composition to obtain an accept fraction and a reject fraction; and dewatering the accept fraction output from the screening by a screw press.

1 . A pulping method comprising:
 impregnating wood chips with an impregnating composition to obtain impregnated wood chips;   refining the impregnated wood chips in at least one refiner to obtain a refined pulp composition, wherein the refined pulp composition has Canadian Standard Freeness (CSF) of at least 350;   screening the refined pulp composition to obtain an accept fraction and a reject fraction;   feeding the accept fraction output from the screening to a screw press at a consistency of 3 to 4%; and   dewatering the accept fraction output from the screening by the screw press to a consistency of at least 20%, wherein the dewatering step provides, as an output, a pulp composition.   
     
     
         2 . The method according to  claim 1 , wherein the dewatering is carried out both during the screening and in the subsequent screw press. 
     
     
         3 . The method according to  claim 1 , wherein in the dewatering, the pulp composition is dewatered to a consistency of at least 30%. 
     
     
         4 . The method according to  claim 1 , further comprising feeding the dewatered accept fraction to a bleaching step, optionally after decreasing the consistency of the pulp composition to less than 15%. 
     
     
         5 . The method according to  claim 1 , wherein the consistency of the accept fraction is first increased to above 20% and then decreased to about 8 to 12% to clean the pulp composition. 
     
     
         6 . The method according to  claim 1 , wherein the screening is carried out by a first screening device and a subsequent second screening device, and wherein the consistency of the pulp composition in the output of the first screening device is lower than the consistency of the pulp composition in the output of the second screening device. 
     
     
         7 . The method according to  claim 1 , wherein, in the screening step, at least 50 wt of the refined pulp composition becomes directed to the accept fraction. 
     
     
         8 . The method according to  claim 1 , further comprising directing the reject fraction from the screening step to a reject treatment line; and refining the reject fraction by a reject refiner. 
     
     
         9 . The method according to  claim 8 , further comprising
 directing an output of the reject treatment line to said screw press,   wherein said output of the reject treatment line has a consistency of at least 2%.   
     
     
         10 . The method according to  claim 1 , wherein the impregnating composition is an aqueous composition comprising one or more members selected from the group consisting of: NaOH, Na 2 SO 3 , white liquor, green liquor, and H 2 O 2 . 
     
     
         11 . The method according to  claim 1 , further comprising directing at least part of the reject fraction from the screening step back to said impregnating step or to a step preceding said impregnating step. 
     
     
         12 . The method according to  claim 1 , wherein the method produces a chemithermomechanical pulp or a bleached chemithermomechanical pulp. 
     
     
         13 . A pulp composition, obtained by a pulp manufacturing process incorporating the method of  claim 1 . 
     
     
         14 . A system configured to execute the method according to  claim 1 , the system forming part of a pulp mill and comprising:
 a wood chipping device;   a wood chip impregnating system;   one or more primary refiners;   one or more pulp screening devices;   a pulp dewatering device which is a screw press; and   optionally a pulp bleaching system.