Four stage alkaline peroxide mechanical pulping

Abstract

A process for applying chemicals, such as an alkaline peroxide pretreatment ( 1 ) to lignocellulosic material before chemical refining and at the primary refiner ( 3 ). The preferred embodiment comprises (i) preconditioning at temperatures below 95° C., especially below 80° C., (ii) limiting the time and/or temperature in the refiner, (iii) reaction quench to maintain temperatures below 80° C., and (iv) subsequent high consistency bleaching ( 4 ).

What is claimed is:  
     
         1 . An alkaline peroxide mechanical pulping process comprising the steps of: 
 feeding a lignocellulosic material into a first press;    pressing the lignocellulosic material;    discharging the lignocellulosic material from the first press;    impregnating the lignocellulosic material discharged from the first press with a first alkaline peroxide pretreatment solution and maintaining the impregnation for a first reaction time;    feeding the lignocellulosic material impregnated with the first pretreatment solution to a refiner having an inlet and a rotating disc within a casing;    adding an alkaline peroxide refiner solution to the lignocellulosic material as it fed to the refiner;    mixing the refiner solution and the lignocellulosic material with the refiner as the material is refined to a primary pulp;    delivering the primary pulp from the refiner casing to a high consistency tower;    retaining the primary pulp in the tower to produce bleached primary pulp; and    further processing the bleached primary pulp to a secondary pulp.    
     
     
         2 . The alkaline peroxide mechanical pulping process of  claim 1  further comprising; 
 feeding the lignocellulosic material that has been impregnated with the first pretreatment solution for a first reaction time, into a second press;  
 pressing and discharging the lignocellulosic material from the second press;  
 impregnating the lignocellulosic material discharged from the second press with a second alkaline peroxide pretreatment solution and maintaining the second impregnation for a second reaction time.  
 
     
     
         3 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the first pretreatment solution impregnation is at a temperature of about 0° C. to about 90° C. and is maintained for said first reaction time of about 5 to about 45 minutes.  
     
     
         4 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein 
 the first pretreatment solution comprises up to about 0.5% chelation agent based on dried material weight, up to about 4% NaOH based on dried material weight, and up to about 4% H2O2 based on dried material weight; and    about 0% to about 4% sodium silicate based on dried material weight, and    about 0% to about 2% MgSO4 based on dried material weight.    
     
     
         5 . The alkaline peroxide mechanical pulping process of  claim 2 , wherein the second pretreatment solution impregnation is at a temperature of about 10° C. to about 80° C. maintained for said second reaction time of about 5 to about 60 minutes.  
     
     
         6 . The alkaline peroxide mechanical pulping process of  claim 2 , wherein the second pretreatment solution comprises; 
 up to about 0.5% chelation agent based on dried material weight, about 0.5% to about 6% NaOH based on dried material weight, about 0.5% to about 6% H2O2 based on dried material weight; and    about 0% to about 4% sodium silicate based on dried material weight; and    about 0% to about 2% MgSO4 based on dried material weight.    
     
     
         7 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the refiner solution comprises; 
 up to about 0.5% chelation agent based on dried material weight, up to about 4% NaOH based on dried material weight, and up to about 4% H2O2 based on dried material weight; and    about 0% to about 4% sodium silicate based on dried material weight; and    about 0% to about 2% MgSO4 based on dried material weight.    
     
     
         8 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the refiner has an atmospheric pressure at the inlet and the casing.  
     
     
         9 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the refiner inlet is maintained at atmospheric pressure and the casing is maintained at a pressure above atmospheric.  
     
     
         10 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the refiner casing is maintained at a gauge pressure of at least about 0.5 bar.  
     
     
         11 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the step of delivering the primary pulp from the refiner casing to the high consistency tower further comprises cooling the primary pulp with water as it is delivered.  
     
     
         12 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the step of delivering the primary pulp from the refiner casing to the high consistency tower is through a blow valve.  
     
     
         13 . The alkaline peroxide mechanical pulping process of  claim 12 , further comprising the step of delivery the primary pulp from the blow valve to a mixing screw, mixing the primary pulp with the screw, and adding water to the primary pulp as the primary pulp is mixed.  
     
     
         14 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the refiner has a pressure above atmospheric at the inlet and a pressure above atmospheric in the casing.  
     
     
         15 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the material is retained in the high consistency tower for a retention time of about 15 minutes.  
     
     
         16 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the step of adding a refiner solution to the lignocellulosic material as it is fed to the refiner occurs at a cross conveyor between the first press and the refiner.  
     
     
         17 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the step of adding a refiner solution to the lignocellulosic material as it is fed to the refiner occurs at a ribbon feeder at the refiner inlet.  
     
     
         18 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the step of adding a refiner solution to the lignocellulosic material as it is fed to the refiner occurs at the inlet of the refiner plates.  
     
     
         19 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the step of pressing the lignocellulosic material impregnated with the first pretreatment solution is accomplished with the first press having a compression ratio of at least about 1.5:1.  
     
     
         20 . The alkaline peroxide mechanical pulping process of  claim 2 , wherein the step of pressing the lignocellulosic material impregnated with the second pretreatment solution is accomplished with the second press having a compression ratio of at least about 1.5:1.  
     
     
         21 . The alkaline peroxide mechanical pulping process of  claim 1 , wherein the material at the first impregnation with the first impregnation solution is in the form of wood chips having a consistency of about 15% to about 50%.  
     
     
         22 . The alkaline peroxide mechanical pulping process of  claim 2 , wherein the material is in the form of wood chips and the chips at the second impregnation with the second impregnation solution have a consistency of about 20% to about 50%.  
     
     
         23 . The alkaline peroxide mechanical pulping process of  claim 2 , wherein the material at the first impregnation with the first impregnation solution is in the form of wood chips having a consistency of about 15% to about 50%, and the chips at the second impregnation with the second impregnation solution have a consistency of about 20% to about 50%  
     
     
         24 . An alkaline peroxide mechanical pulping process comprising the steps of: 
 feeding a lignocellulosic material into a first press;    pressing the lignocellulosic material;    discharging the lignocellulosic material from the first press;    impregnating the lignocellulosic material discharged from the first press with a first alkaline peroxide pretreatment solution and maintaining the impregnation for a first reaction time;    feeding the lignocellulosic material impregnated with the first pretreatment solution to a refiner having an inlet and a rotating disc within a casing;    adding an alkaline peroxide refiner solution to the lignocellulosic material at the refiner;    mixing the refiner solution and the lignocellulosic material with the refiner as the material is refined; and    discharging the lignocellulosic material from the casing and maintaining the discharged lignocellulosic material at conditions that allow continued peroxide bleaching of the primary pulp.    
     
     
         25 . A chemimechanical pulping process comprising the steps of: 
 feeding a lignocellulosic material into a first atmospheric press;    pressing the lignocellulosic material;    discharging the lignocellulosic material from the first press;    impregnating the lignocellulosic material discharged from the first press with a first chemical bleaching pretreatment solution and maintaining the impregnation for a first reaction time;    feeding the lignocellulosic material impregnated with the first pretreatment solution to a refiner having an inlet and a rotating disc within a casing;    adding a chemical refiner bleaching solution to the lignocellulosic    material at the refiner;    mixing the refiner solution and the lignocellulosic material with the refiner as the material is refined to a primary pulp;    discharging the primary pulp from the casing to a high consistency tower;    maintaining the discharged primary pulp at conditions to reduce chemical reactions extraneous to bleaching of the primary pulp; and    processing the primary pulp further to a secondary pulp.