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.

1 . A method useful in a pulping process that produces a byproduct liquor, said method comprising the steps of: 
 a) determining the relationship between the amount of oxygen-containing gas injected into a reactor containing the byproduct liquor or the amount of stripping steam generated in said reactor and the amount of methanol generated in said reactor;    b) injecting oxygen-containing gas into said reactor comprising the byproduct liquor, such that said injecting results in both a further concentrated liquor and a stripping gas, said stripping gas comprising both water vapor and methanol;    c) stopping said injecting of said oxygen-containing gas at a point of required conversion of the sulfides when: (i) continued injection of said oxygen-containing gas results in methanol production at a faster rate than it can be removed by said stripping gas, or (ii) both at a point that is at or after the point of required conversion of the sulfides and prior to a point at which said oxygen-containing gas reacts to form methanol at a faster rate than is removed by said stripping gas; and    d) separating said stripping gas from said further concentrated liquor.    
   
   
       2 . The method according to  claim 1  further comprising: 
 e) condensing said water vapor from said stripping gas so as to produce a condensate comprising said methanol.    
   
   
       3 . The method according to  claim 1  wherein after said step (c) is the additional step of injecting a second oxygen-containing gas into said reactor comprising the byproduct liquor, such that said injecting results in both a further concentrated liquor and a second stripping gas, said second stripping gas comprising both water vapor and methanol.  
   
   
       4 . The method according to  claim 1  wherein after said step (c) is the additional step of injecting a non-oxidative gas into said reactor comprising the byproduct liquor, such that said injecting results in both a further concentrated liquor and a second stripping gas, said second stripping gas comprising both water vapor and methanol.  
   
   
       5 . The method according to  claim 1  wherein after step (d), steps (a), (b), (c) and (d) are repeated for a second reactor downstream of said first reactor into which said further concentrated liquor is fed.  
   
   
       6 . The method according to  claim 5  wherein for said repeated steps (a), (b), and (c) for said second reactor, a second oxygen-containing gas is injected.  
   
   
       7 . The method according to  claim 1  further comprising the steps of: 
 e) feeding said further concentrated liquor into a second reactor; and    f) injecting a non-oxidative gas into said second reactor.    
   
   
       8 . The method according to  claim 4  wherein said non-oxidative gas is selected from the group of steam and an inert gas.  
   
   
       9 . The method of  claim 1  wherein said oxygen-containing gas is air.  
   
   
       10 . The method of  claim 1  wherein said oxygen-containing gas comprises at least 70% (v/v) oxygen.  
   
   
       11 . The method of  claim 1  wherein the oxygen-containing gas comprises an inert gas at a concentration of 1% to 40% v/v.  
   
   
       12 . The method of  claim 1  wherein subsequent to step (c) the liquor is processed in a flash tank so as to produce a further concentrated liquor and both water vapor and methanol.  
   
   
       13 . A method of  claim 1  wherein the oxygen-containing gas in step (b) is the oxygen-richer gas, and wherein at a time prior to step (b), 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.  
   
   
       14 . A method of  claim 13  wherein the oxygen-poorer gas is air.  
   
   
       15 . A method of  claim 1  which further comprises combining, with new byproduct liquor that has not yet been processed through steps (b) and (c), 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 (b) (c) and (d).  
   
   
       16 . A method of  claim 1  wherein step (d) occurs at a pressure of greater than  2  bar(g).  
   
   
       17 . A method of  claim 1  which further comprises combining, with new byproduct liquor that has not yet been processed through steps (b) and (c), 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 processing at least a portion of said mixture through the steps (b), (c) and (d) described for a byproduct liquor, wherein step (b) is done at temperatures less than 175° C.  
   
   
       18 . The method of  claim 17 , wherein subsequent to step (d) occurs in a flash tank so as to create a cooled liquor.  
   
   
       19 . A method of  claim 17  wherein step (b) is done at a temperature less than 150° C.  
   
   
       20  A method of  claim 17  wherein step (b) takes place in a pressurized reactor operating at greater than 2.0 bar(g).