Removing SO.sub.x, NO.sub.X and CO from flue gases

A method of removing nitrogen oxide, sulfur oxide and carbon monoxide from a combustion flue gas stream from a fluid catalytic cracking unit comprising a FCC reactor for converting a stream of petroleum feedstock in the presence of a fluidized bed of cracking catalyst into a stream of cracked product, a FCC regenerator for combusting coke buildup and other products from spent catalyst to thereby regenerate the spent catalyst and provide the combustion flue gas stream, a conduit for feeding spent catalyst from the FCC reactor to the FCC regenerator, and another conduit for passing regenerated catalyst from the FCC regenerator to the FCC reactor comprising the steps of:

• combusting said coke buildup deposited on the spent catalyst in said FCC regenerator with a reduced amount of oxygen-containing gas ranging from about 95% to about 110% of the stoichiometric amount required to convert carbon monoxide into carbon dioxide to partially convert carbon monoxide therein to carbon dioxide and sufficient to convert all sulfur-containing species therein to sulfur oxide, and thus forming a sulfur oxide containing flue gas stream having at least 500 ppm carbon monoxide and the amount of nitrogen oxide in the sulfur oxide containing gas is an inverse function of the amount of carbon monoxide therein when the amount of oxygen containing gas fed to the combustor is reduced relative to the amount of oxygen containing gas needed to oxide all the carbon monoxide into carbon dioxide;
• contacting said sulfur oxide containing flue gas stream and sufficient additional air with a solid adsorbent bed for adsorbing thereon the sulfur oxides in the form of inorganic sulfates or sulfur oxides or combinations thereof, the solid adsorbent containing a catalytic oxidation promoter for oxidizing the carbon monoxide in said sulfur oxide containing gas stream to carbon dioxide, and thus forming a sulfur oxide and carbon monoxide depleted stream for disposal;
• and
• contacting said adsorbent bed with a reducing gas stream for regenerating said adsorbent bed by reducing said retained inorganic sulfates or sulfur oxides or combinations thereof to hydrogen sulfide and/or sulfur dioxide, and thereby forming a hydrogen sulfide and/or sulfur dioxide bearing stream.