Method and system for controlling the addition of oxygen gas and alkali during oxygen gas delignification

Abstract

The method and system is for the acid gas delignification of cellulose pulp in a gas/fluid suspension. The oxygen gas delignification takes place in a reactor system with one or several oxygen gas reactors. Delignification chemicals are added at least before the first oxygen gas reactor such that oxygen gas remains present during the complete reaction process in the reactors. Alkali in an amount that ensures that the pH lies above 9 is also added. The temperature of the cellulose pulp is measured at two different positions (T 1 , T 2 , . . . , Tn) viewed in the direction of flow of the pulp though the system. The measurements are used to control the charged amount of the delignification chemicals to the oxygen gas delignification. The first temperature measurement (T 1 ) is carried out at a position in association with the first addition of oxygen gas.

1 . A method for an oxygen gas delignification of cellulose pulp in a gas/fluid suspension in which the oxygen gas delignification takes place in a reactor system with oxygen gas reactor, comprising: 
 providing delignification chemicals in such a quantity that oxygen gas remains present during a complete reaction process in the oxygen gas reactor;    together with the oxygen gas, providing alkali at an amount that ensures that a pH value in the oxygen gas reactor remains over 9;    adding the oxygen as and alkali upstream of the oxygen gas reactor;    measuring a temperature of the cellulose pulp at a start of the oxygen gas delignification at two different locations to determine an initial consumption of delignification chemicals that have reacted in a fluid phase,    using the determined initial consumption of delignification chemicals to control or adjust an amount of at least one delignification chemical charged to the oxygen gas delignification    reducing or increasing an amount of delignification chemicals charged while at the same time ensuring a presence of delignification chemicals during the complete reaction process.    
   
   
       2 . The method according to  claim 1 , wherein positions of measurements between two subsequent temperature measurements correspond to positions between which the cellulose pulp has had a retention time in the reactor system between 10 seconds and 30 minutes.  
   
   
       3 . The method according to  claim 1  wherein a first temperature measurement is made at a location after the addition of oxygen gas.  
   
   
       4 . The method according to  claim 1  wherein a first temperature measurement is made at a location before the addition of oxygen gas.  
   
   
       5 . The method according to  claim 1  wherein two temperature measurements are made and that a derivative between the first and the second temperature measurement is used to control an amount charged of at least one delignification chemical.  
   
   
       6 . The method according to  claim 1  wherein temperature measurements are coupled to an oxygen gas trend that is used to control an amount charged of at least one delignification chemical.  
   
   
       7 . A system for an oxygen gas delignification of cellulose pulp in a gas/fluid suspension in which the oxygen gas delignification takes place in a reactor system, comprising: 
 an oxygen gas reactor having delignification chemicals contained therein;    an alkali addition location for adding alkali to the system, the alkali addition location being upstream of the oxygen gas reactor;    a delignification chemicals addition location for adding delignification chemicals to the system, the delignification chemicals addition location being upstream of the oxygen gas reactor;    a first temperature sensor located adjacent to the delignification chemicals addition location;    a second temperature sensor located in the reactor system downstream of the first temperature sensor;    the first and second temperature sensors being electrically connected to a control unit;    the control unit being electrically connected to a control valve; and    the control valve being in operative engagement with a delignification chemicals supply to control a flow of delignification chemicals to the delignification chemicals addition location.    
   
   
       8 . The system according to  claim 7  wherein the first temperature sensor, viewed from a flow direction of the cellulose pulp through the system, is located immediately downstream of the delignification chemicals addition location.  
   
   
       9 . The system according to  claim 7  wherein the first temperature sensor, viewed from a flow direction of the cellulose pulp through the system, is located immediately upstream of the delignification chemicals addition location.