Methods for oxygen delignification and ozone bleaching of pulp

Abstract

A method for treating pulp through oxygen delignification and ozone bleaching is disclosed. The method uses a modified oxygen recovery unit which separates a mixture of oxygen and ozone thereby generating a stream of ozone and a stream of oxygen; feeding the stream of oxygen to an oxygen delignification unit; feeding a pulp to the oxygen delignification unit; feeding the stream of ozone to an ozone bleaching unit; feeding the delignified pulp to the ozone bleaching unit; and recovering the delignified and bleached pulp.

What we claim is: 
     
         1 . A method for delignifying and bleaching pulp comprising the steps:
 a) Feeding a mixture of oxygen and ozone to an oxygen recovery unit thereby generating a stream of ozone and air and a stream of oxygen;   b) Compressing and feeding the stream of oxygen to an oxygen delignification unit;   c) Feeding a pulp mixture which comprises a pulp slurry and a liquor to the oxygen delignification unit;   d) Feeding steam to the pulp mixture thereby raising its temperature;   e) Mixing the pulp mixture of pulp, liquor, steam and oxygen thereby enabling the oxygen to react with lignin and become water soluble and mixed with the liquor;   f) Feeding the pulp mixture to at least one washing step thereby removing dissolved lignin from the pulp mixture;   g) Feeding the stream of air and ozone to an ozone bleaching unit;   h) Feeding the delignified, washed pulp mixture of step f) to the ozone bleaching unit; and   i) Recovering the delignified and bleached pulp.   
     
     
         2 . The method as claimed in  claim 1  wherein the pressure in step b) ranges from 5 to 12 Barg. 
     
     
         3 . The method as claimed in  claim 1  wherein during step c), the temperature of the pulp mixture increases from about 90° to 120° C. 
     
     
         4 . The method as claimed in  claim 1  wherein the mixing is up to 100 minutes in length. 
     
     
         5 . The method as claimed in  claim 1  wherein the at least one washing step is two or more washing steps. 
     
     
         6 . The method as claimed in  claim 1  wherein the pulp is selected from the group consisting of medium and high consistency pulp. 
     
     
         7 . The method as claimed in  claim 1  wherein the liquor is selected from the group consisting of white liquor, partially oxidized white liquor and completely oxidized white liquor. 
     
     
         8 . The method as claimed in  claim 1  wherein the concentration of oxygen in the stream of oxygen is greater than 80%. 
     
     
         9 . The method as claimed in  claim 1  wherein the oxygen delignification unit is a reactor. 
     
     
         10 . The method as claimed in  claim 9  wherein the oxygen is present in the pulp between 0.011 to 0.026 tons of oxygen per one ton of pulp. 
     
     
         11 . The method as claimed in  claim 1  wherein the mixture of oxygen and ozone is produced by an ozone generation unit. 
     
     
         12 . The method as claimed in  claim 10  wherein the mixture of oxygen and ozone is about 10% ozone and 90% oxygen. 
     
     
         13 . The method as claimed in  claim 1  wherein the oxygen recovery unit is a pressure swing adsorption system. 
     
     
         14 . The method as claimed in  claim 13  wherein the pressure swing adsorption system contains an adsorbent. 
     
     
         15 . The method as claimed in  claim 14  wherein the adsorbent is selected from the group consisting of silica gel and high silica zeolite. 
     
     
         16 . The method as claimed in  claim 1  wherein the ozone bleaching unit is a reactor. 
     
     
         17 . The method as claimed in  claim 6  wherein the pulp is about 10% consistency. 
     
     
         18 . The method as claimed in  claim 1  further comprising adding acid to the pulp before the pulp enters the ozone bleaching unit.