Method and apparatus for NOx and Hg removal

Abstract

A cyclic process for the removal of NO x from a NO x containing feed gas, and optionally removal mercury vapour and/or sulfur dioxide is provided. A process is also provided by which an iron chelate absorbent may be thermally regenerated.

1 - 37 . (canceled)  
   
   
       38 . A cyclic process for the removal of NO x  and Hg 0  from a NO x  and Hg 0  containing feed gas stream using an iron amine polycarboxylic acid chelate absorbent and for the regeneration of the absorbent, which comprises: 
 a. contacting the feed gas stream with the absorbent to form a NO x  reduced gas stream and a spent NO x  absorbent;    b. contacting the NO x  reduced gas stream in a second contacting step with an oxidizing agent to convert Hg 0  to an ionic form of mercury and absorbing the ionic mercury in the oxidizing agent;    c. recovering the spent NO x  absorbent;    d. treating the spent NO x  absorbent to remove NO x  and forming a regenerated absorbent; and,    e. recycling the regenerated NO x  absorbent to the contacting steps.    
   
   
       39 . The process of  claim 38  further comprising absorbing mercury in the chelate absorbent and treating the spent NO x  absorbent to also remove mercury.  
   
   
       40 . The process of  claim 39  further comprising treating the spent NO x  absorbent to recover mercury prior to regenerating the absorbent.  
   
   
       41 . The process of  claim 40  wherein mercury is removed from the spent NO x  absorbent by at least one of ion exchange and precipitation.  
   
   
       42 . The process of  claim 38  further comprising selecting the oxidizing agent from a ferric salt in acidic solution, potassium permanganate aqueous solution, sodium hypochlorite aqueous solution and mixtures thereof.  
   
   
       43 . The process of  claim 38  further comprising treating the feed gas stream to oxidize Hg 0  and obtain ionic mercury in a water prescrubber prior to step (a).  
   
   
       44 . A cyclic process for the removal of NO x  and Hg 0  from a NO x  and Hg 0  containing feed gas stream using an iron amine polycarboxylic acid chelate absorbent and for the regeneration of the absorbent, which comprises: 
 a. contacting the feed gas stream with the absorbent to form a NO x  and mercury reduced gas stream and a spent absorbent;    b. recovering the spent absorbent;    c. treating the spent absorbent to recover mercury prior to regenerating the absorbent;    d. treating the spent absorbent to remove NO x  and forming a regenerated absorbent; and,    e. recycling the regenerated absorbent to the contacting step.    
   
   
       45 . The process of  claim 44  wherein mercury is removed from the spent absorbent by at least one of ion exchange and precipitation.  
   
   
       46 . The process of  claim 44  further comprising treating the iron chelate such that 20 to 90 weight % is in the Fe 2+  state prior to the absorbent contacting the feed and 80-10 weight % is in the Fe 3+  state.  
   
   
       47 . The process of  claim 44  further comprising treating the iron chelate such that 30 to 65 weight % is in the Fe 2+  state prior to the absorbent contacting the feed and 70-35 weight % is in the Fe 3+  state.  
   
   
       48 . A cyclic process for the removal of NO x  from a NO x  containing feed gas stream using an iron amine polycarboxylic acid chelate absorbent and for the regeneration of the absorbent, which comprises: 
 a. contacting the feed gas stream with the absorbent to form a NO x  rich absorbent;    b. thermally treating the NO x  rich absorbent to remove NO x  and to form a regenerated absorbent; and,    c. recycling the regenerated absorbent to the contacting step.    
   
   
       49 . The process as claimed in  claim 48  wherein the absorbent is thermally regenerated by steam stripping.  
   
   
       50 . The process of  claim 49  wherein the NO x  rich absorbent is at a pH of 4-6.  
   
   
       51 . The process of  claim 49  wherein the NO x  rich absorbent is at a pH of 5-6.  
   
   
       52 . A cyclic process for the removal of NO x  and Hg 0  from a NO x  and Hg 0  containing feed gas stream using an iron amine polycarboxylic acid chelate absorbent and for the regeneration of the absorbent, which comprises: 
 a. treating the feed gas stream to oxidize Hg 0  and obtain ionic mercury in a water prescrubber using an oxidizing agent;    b. contacting the feed gas stream with the absorbent to form a NO x  and mercury reduced gas stream and a spent absorbent;    c. recovering the spent absorbent; and,    d. regenerating and recycling the spent absorbent.    
   
   
       53 . The process as claimed in  claim 52  further comprising treating the spent absorbent to recover mercury therefrom and obtaining a mercury lean spent absorbent prior to removing NO x  from the spent absorbent.  
   
   
       54 . The process as claimed in  claim 53  further comprising treating the mercury lean spent absorbent to remove NO x  and forming a regenerated absorbent.  
   
   
       55 . The process of  claim 52  wherein the absorbent comprises an iron chelate and the iron chelate is thermally regenerated.  
   
   
       56 . The process of  claim 52  further comprising treating the iron chelate such that 20 to 90 weight % is in the Fe 2+  state prior to the absorbent contacting the feed and 80-10 weight % is in the Fe 3+  state.  
   
   
       57 . The process as claimed in  claim 53  further comprising select ferric ions as the oxidizing agent.  
   
   
       58 . The process of  claim 55  further comprising treating the iron chelate such that 30 to 65 weight % is in the Fe 2+  state prior to the absorbent contacting the feed and 70-35 weight % is in the Fe 3+  state.