Method and a device for preparing cellulose pulp

Abstract

A method and an apparatus for preparing cellulose pulp, in which a lignin-containing raw material is impregnated with impregnation liquor and the impregnated raw material is cooked. The black liquor obtained by cooking is concentrated in an evaporation plant integrated in a chemical recovery plant. In the impregnation, the lignin-containing raw material is impregnated with a circulating alkaline impregnating liquor, which impregnating liquor is concentrated by evaporating water from it in at least one evaporator unit of the evaporation plant arranged in the chemical recovery plant of a pulp mill.

1 . A method for preparing cellulose pulp, the method comprising the steps of: 
 impregnating chipped lignin-containing raw material with a circulating alkaline impregnation liquor;    cooking the chipped lignin-containing raw material impregnated with circulating alkaline impregnation liquor, and obtaining cellulose fibers and black liquor as a result of said cooking;    concentrating the black liquor obtained from cooking by evaporation in a evaporation plant integrated in a chemical recovery plant of a pulp mill; and    wherein the circulating alkaline impregnation liquor is concentrated by evaporating water from said circulating alkaline impregnation liquor in at least one evaporator unit of the evaporation plant arranged in the chemical recovery plant of the pulp mill.    
   
   
       2 . The method of  claim 1 , further comprising the step of before the circulating impregnation liquor is concentrated, adding white liquor to the circulating impregnation liquor.  
   
   
       3 . The method of  claim 1 , wherein the concentrated impregnating liquor is led from the at least one evaporator unit into an impregnation liquor tank which is an existing tank in the evaporation plant.  
   
   
       4 . The method of  claim 1 , further comprising the step of removing soap accumulating on the concentrated circulating alkaline impregnation liquor in the impregnation liquor tank.  
   
   
       5 . The method of  claim 1 , wherein the impregnation step comprises a first impregnation step and a second impregnation step.  
   
   
       6 . The method of  claim 5 , wherein the concentrated circulating alkaline impregnation liquor is led from the impregnation liquor tank to the first impregnation step and then to the second impregnation step.  
   
   
       7 . The method of  claim 6 , wherein the concentrated circulating alkaline impregnation liquor is heated before it is used in the second impregnation step.  
   
   
       8 . The method of  claim 5 , wherein the lignin-containing raw material is impregnated downstream in the first impregnation step and upstream in the second impregnation step.  
   
   
       9 . The method of  claim 5 , wherein the temperature in the first impregnation step is adjusted to between 100 to 170° C. and the first impregnation step takes about 15 to 120 min, and the second impregnation step takes about 5 to 60 minutes.  
   
   
       10 . The method of  claim 1 , wherein the circulating alkaline impregnation liquor is obtained from the impregnation step, and is concentrated in the at least one evaporator unit of the evaporation plant; and 
 wherein the evaporation plant has a plurality of evaporator units heated by a common heating medium circulation and the at least one evaporator unit of the evaporation plant is also heated by the common heating medium circulation.    
   
   
       11 . The method of  claim 1 , wherein the circulating alkaline impregnation liquor is obtained from the impregnation step and is concentrated in the at least one evaporator unit of the evaporation plant, and wherein the evaporator plant has a circulation of black liquor therein and wherein the at least one evaporator unit is separate from the circulation of black liquor in the evaporation plant.  
   
   
       12 . The method of  claim 10 , wherein secondary steam released by the step of concentrating the circulating alkaline impregnation liquor is used as a heating medium in the common heating medium circulation.  
   
   
       13 . The method of  claim 1 , further comprising the steps of: 
 before the step of impregnating, removing gas by treating the chipped lignin containing raw material with steam;    after the step of cooking the chipped lignin containing raw material, washing the cellulose fibers obtained by cooking.    
   
   
       14 . An apparatus for preparing cellulose pulp, the apparatus comprising: 
 an impregnating means for impregnating a chopped lignin containing raw material with alkaline impregnation liquor; and    a cooking means for cooking the chopped lignin containing raw material impregnated with alkaline impregnation liquor; and    an evaporation plant integrated in a chemical recovery plant, connected to the cooking means in black liquor receiving relation, the evaporation plant arranged for concentrating black liquor received from the cooking means, wherein the evaporation plant has at least one evaporator unit arranged for receiving and concentrating impregnation liquor, and connected in concentrated impregnation liquor supplying relation to the impregnation means.    
   
   
       15 . The apparatus of  claim 14 , further comprising at least one line arranged to circulate alkaline impregnation liquor from the impregnation means to the at least one evaporator unit.  
   
   
       16 . The apparatus of  claim 14  further comprising at least one line arranged to circulate alkaline impregnation liquor from the at least one evaporator unit to the impregnation means.  
   
   
       17 . The apparatus of  claim 14 , further comprising a source of white liquor connected to the at least one line arranged to circulate alkaline impregnation liquor from the impregnation means to the at least one evaporator unit.  
   
   
       18 . The apparatus of  claim 14 , further comprising an impregnation liquor tank formed from an existing tank in the evaporation plant, connected in concentrated impregnating liquor receiving relation to the at least one evaporator unit arranged for receiving and concentrating impregnation liquor.  
   
   
       19 . The apparatus of  claim 18 , further comprising a soap discharge line connected to the impregnation liquor tank and leading to a soap discharge.  
   
   
       20 . The apparatus of  claim 14 , wherein the impregnating means is divided into a first impregnation part and a second impregnation part.  
   
   
       21 . The apparatus of  claim 20 , further comprising a first concentrated impregnation liquor line leading from the impregnation liquor tank to the first impregnation part, and a second concentrated impregnation liquor line leading from the impregnation liquor tank to the second impregnation part.  
   
   
       22 . The apparatus of  claim 21 , further comprising a heat exchanger arranged in the first impregnation liquor line between the impregnation liquor tank and the second impregnation part, for heating concentrated impregnation liquor.  
   
   
       23 . The apparatus of  claim 20 , wherein impregnation in the first impregnation part is arranged to be done downstream; and 
 wherein impregnation in the second impregnation part is arranged to be done upstream.    
   
   
       24 . The apparatus of  claim 14 , wherein the impregnation means contains concentrated impregnation liquor and chopped lignin containing raw material at a temperature of 100 to 170° C.  
   
   
       25 . The apparatus of  claim 14 , wherein a heating medium circulation system is arranged to supply heat to the evaporation plant, including the at least one evaporator unit.  
   
   
       26 . The apparatus of  claim 14 , wherein the at least one evaporator unit of the evaporation plant is not connected to the cooking means in black liquor receiving relation.  
   
   
       27 . The apparatus of  claim 25 , wherein an expansion steam line is arranged extending from the at least one evaporator unit to the heating medium circulation system of the the evaporation plant.  
   
   
       28 . The apparatus of  claim 14 , further comprising: 
 a gas removal means for removing gases from chipped lignin containing raw material arranged to supply the impregnating means; and    washing means for washing cellulose fiber arranged in cellulose fiber receiving relation to the cooking means.