Method to lower the release of hazardous air pollutants from kraft recovery process

Abstract

A method for removal of pollutants from a pulping process byproduct liquor, the method comprising injecting an oxygen-containing gas into said liquor and condensing the water vapor from the stripping gas so as to produce a condensate comprising pollutants. Also a method of controlling the flow rate and/or temperature of a pulping process byproduct liquor, the process comprising injecting an oxygen-containing gas into the liquor in a reactor, processing the liquor in a flash tank so as to create a cooled liquor and combining at a least a portion of the cooled liquor with new liquor as the new liquor enters, or while the new liquor is in, the reactor.

1 . In a pulping process that employs a multiple effect evaporator such that said evaporator produces a byproduct liquor, the improvement that comprises: 
 a) injecting an amount of oxygen-containing gas into a reactor, said gas comprising oxygen, said oxygen at a concentration at least 22% (v/v), such that said injecting results in greater than 40% of said oxygen reacting with the components of the liquor and such that said injecting results in both a further concentrated liquor and a stripping gas comprising both water vapor and methanol that was in the liquor prior to step (a);    b) condensing said water vapor from said stripping gas so as to produce a condensate comprising said methanol; and    c) separating said condensate from said further concentrated liquor.    
     
     
         2 . A method of  claim 1  wherein said oxygen-containing gas comprises at least 70% (v/v) oxygen.  
     
     
         3 . A method of  claim 2  wherein said oxygen-containing gas comprises at least 95% (v/v) oxygen.  
     
     
         4 . A method of  claim 1  wherein at least 70% of the oxygen in the oxygen containing gas reacts with the components of the liquor.  
     
     
         5 . A method of  claim 2  wherein at least 95% of the oxygen in the oxygen-containing gas reacts with the components of the liquor.  
     
     
         6 . A method of  claim 1  wherein said oxygen-containing gas comprises at least 70% (v/v) oxygen and wherein at least 70% of the oxygen in the oxygen-containing gas reacts with the components of the liquor.  
     
     
         7 . A method of  claim 1  wherein said oxygen-containing gas comprises at least 95% (v/v) oxygen and wherein at least 95% of the oxygen in the oxygen-containing gas reacts with the components of the liquor.  
     
     
         8 . A method of  claim 1  wherein the liquor contains about 40%-55% solids (w/w).  
     
     
         9 . A method of  claim 1  wherein the oxygen-containing gas comprises an inert gas at a concentration of 1% to 40% v/v.  
     
     
         10 . The method of  claim 1  wherein subsequent to step (a) the liquor is processed in a flash tank so as to produce a further concentrated liquor and both water vapor and methanol and wherein said water vapor is condensed to produce a condensate comprising said methanol, and wherein said condensate is separated from said further concentrated liquor.  
     
     
         11 . A method of  claim 1  wherein the oxygen-containing gas in step (a) is the oxygen-richer gas, and wherein at a time prior to step (a), there is a step comprising injecting an oxygen-containing gas into said concentrated liquor, said gas being the oxygen-poorer gas by virtue of the fact that it contains a lower percentage of oxygen than the oxygen-richer gas does.  
     
     
         12 . A method of  claim 10  wherein the oxygen-poorer gas is air.  
     
     
         13 . A method of  claim 1  which further comprises combining, with new byproduct liquor that has not yet been processed through steps (a) and (b), at least a portion of the further concentrated liquor so as create a mixture of said new byproduct liquor and said portion of further concentrated liquor and, subsequent to said combining, processing at least a portion of said mixture through the steps (a), (b) and (c) described for a byproduct liquor.  
     
     
         14 . A method of  claim 1  wherein the majority of inert gases and unreacted oxygen in the oxygen-containing gas are separated from the by-product liquor at a point subsequent to reaction of the oxygen at a pressure of greater than 2 bar(g).  
     
     
         15 . In a pulping process that employs a multiple effect evaporator such that said evaporator produces a byproduct liquor, the improvement that comprises controlling the flow rate and/or temperature of the liquor, said improvement comprising: 
 a) injecting an oxygen-containing gas into said liquor, said liquor being in a reactor designed for said purpose;    b) subsequent to step (a), processing the liquor in a flash tank so as to create a cooled liquor; and    c) combining at a least a portion of said cooled liquor with new liquor either previous to said new liquor entering, as said new liquor enters, or while said new liquor is in, said reactor;    wherein step (a) is done at temperatures less than 175° C.    
     
     
         16 . A method of  claim 15  wherein step (a) is done at a temperature less than 150° C.  
     
     
         17 . A method of  claim 15  wherein step (a) is done at a temperature in the range 120 to 135° C.  
     
     
         18 . A method of  claim 15  wherein the oxidation of the liquor takes place in a pressurized reactor operating at greater than 2.0 bar(g).  
     
     
         19 . A method of  claim 15  wherein said oxygen-containing gas comprises at least 70% (v/v) oxygen.  
     
     
         20 . A method of  claim 19  wherein said oxygen-containing gas comprises at least 95% (v/v) oxygen.  
     
     
         21 . A method of  claim 15  wherein the liquor contains about 30%-55% solids (w/w).