Method for manufacturing mechanical pulp

Abstract

A method for manufacturing mechanical pulp. Raw material of the mechanical pulp is introduced. The raw material is refined in a first refining stage to form the mechanical pulp. The pH of the mechanical pulp is adjusted to between 9 and 11 in a process step in which a first process delay is arranged. The first process delay is at least 0.5 hours. The mechanical pulp is sorted into a first accepted stock and a first rejected stock. The first rejected stock is ozonated. The pH of the first rejected stock is at the start of the ozonation process is between 9 and 11. The ozonated first rejected stock is refined in a second refining stage so that at least a part of the ozonated first rejected stock will belong to a second accepted stock. The first accepted stock and the second accepted stock are combined. The mechanical pulp may be used.

1 . A method for manufacturing mechanical pulp, the method comprising:
 introducing raw material of the mechanical pulp,   refining the raw material in a first refining stage to form the mechanical pulp,   adjusting a pH of the mechanical pulp between 9 and 11 in a process step in which a first process delay is arranged, the first process delay being at least 0.5 hours,   sorting the mechanical pulp into a first accepted stock and a first rejected stock,   ozonating the first rejected stock whose pH at the start of the ozonation process is between 9 and 11,   refining the ozonated first rejected stock in a second refining stage so that at least a part of the ozonated first rejected stock will belong to a second accepted stock, and   combining the first accepted stock and the second accepted stock.   
     
     
         2 . The method according to  claim 1 , wherein the first rejected stock is ozonated at a consistency which is higher that 30%. 
     
     
         3 . The method according to  claim 1 , further comprising:
 sorting of the ozonated and refined first rejected stock to the second accepted stock and a second rejected stock.   
     
     
         4 . The method according to  claim 1 , further comprising:
 ozonizing the first accepted stock.   
     
     
         5 . The method according to  claim 4 , wherein the first accepted stock is ozonated at a consistency of from 0.5 to 1.5%. 
     
     
         6 . The method according to  claim 4 , further comprising:
 adding alkali to the ozonated first accepted stock in a process step in which a second process delay is arranged, the second process delay being at least 0.5 hours.   
     
     
         7 . The method according to  claim 1 , further comprising:
 bleaching the first accepted stock and the second accepted stock.   
     
     
         8 . The method according to  claim 1 , further comprising:
 utilizing the mechanical pulp in a paper product manufacturing process.