Integration of Catalytic SO2 Oxidation and Oxyfuel Sour Compression

Abstract

Sulfur dioxide (SO 2 ) may be removed from carbon dioxide feed gas by contacting the carbon dioxide at an elevated temperature and an elevated pressure with a catalyst for oxidizing SO 2 , in the presence of oxygen (O 2 ) to convert SO 2 to sulfur trioxide (SO 3 ); contacting SO 3 in the resultant SO 3 -enriched carbon dioxide gas with water to produce sulfuric acid and SO 2 -depleted carbon dioxide gas; and separating the sulfuric acid from the SO 2 -depleted carbon dioxide gas. If present, NO x is also removed from the carbon dioxide feed gas as nitric acid to produce SO 2 -depleted, NO x -lean carbon dioxide gas. The method has particular application in the removal of SO 2 and NO x from flue gas produced by oxyfuel combustion of a hydrocarbon fuel or carbonaceous fuel, within or downstream of the CO 2 compression train of a CO 2 recovery and purification system.

1 . A method for removing SO 2  and NO x  from carbon dioxide feed gas comprising SO2 and NO x  as contaminants, said method comprising:
 contacting said carbon dioxide feed gas at an elevated temperature and an elevated pressure with a catalyst for oxidizing SO 2 , in the presence of O 2  to convert SO 2  to SO 3  and produce SO 3 -enriched carbon dioxide gas comprising NO x ;   cooling said SO 3 -enriched carbon dioxide gas comprising NO x  to a reduced temperature that is less than the elevated temperature and no more that the acid dew point at said elevated pressure, wherein said gas is maintained at said reduced temperature and elevated pressure(s) in the presence of O 2  and water for a period of time sufficient to convert NO x  to nitric acid, thereby producing SO 2 -depleted, NO x -lean carbon dioxide gas and an aqueous mixed acid solution comprising sulfuric and nitric acids; and   separating said aqueous mixed acid solution from said SO 2 -depleted, NO x -lean carbon dioxide gas, or from a SO 2 -depleted, NO x -lean carbon dioxide gas derived therefrom.   
     
     
         2 . Apparatus for removing SO 2  from carbon dioxide feed gas comprising SO 2  as a contaminant, said apparatus comprising:
 a compressor arrangement for elevating the pressure of carbon dioxide feed gas comprising SO 2  as a contaminant;   a catalytic reactor system comprising a catalyst for oxidizing SO 2 , said reactor system being suitable for contacting carbon dioxide feed gas at an elevated temperature and an elevated pressure with said catalyst in the presence of O 2  to convert SO 2  to SO 3  and produce SO 3 -enriched carbon dioxide gas;   a conduit arrangement for feeding carbon dioxide feed gas at an elevated pressure from said compressor arrangement to said catalytic reactor system;   a separator system for contacting SO 3  in said SO 3 -enriched carbon dioxide gas with water to produce sulfuric acid and SO 2 -depleted carbon dioxide gas, and for separating said sulfuric acid from said SO 2 -depleted carbon dioxide gas, or from a SO 2 -depleted, NO x -lean carbon dioxide gas derived therefrom; and   a conduit arrangement for feeding SO 3 -enriched carbon dioxide gas from said catalytic reactor system to said separator system.   
     
     
         3 . The apparatus of  claim 2  for removing NO x  in addition to SO 2  from said carbon dioxide feed gas comprising NO x  as a further contaminant, wherein nitric acid is produced and separated in the separator system with sulfuric acid to produce SO 2 -depleted, NO x -lean carbon dioxide gas. 
     
     
         4 . The apparatus of  claim 3 , wherein said separator system maintains SO 3 -enriched carbon dioxide comprising NO x  at elevated pressure(s) in the presence of O 2  and water for a period of time sufficient to convert NO x  to nitric acid. 
     
     
         5 . The apparatus of  claim 2  comprising
 an expander arrangement for reducing the pressure of an aqueous acid solution comprising said sulfuric acid to produce said aqueous acid solution at reduced pressure; 
 a conduit arrangement for feeding said aqueous acid solution from said separator system to said expander arrangement; and 
 a conduit arrangement for feeding said aqueous acid solution at reduced pressure from said expander to a flue gas desulfurization system.