Apparatus to reduce NO/sub chi/ emissions from a fluid catalytic cracking unit

This patent describes an apparatus for reducing NO/sub chi/ in flue gas from a regenerator for regenerating a spent fluid catalytic cracking catalyst stream comprising a mixture of ZSM-5 catalyst and zeolite Y catalyst particles from a fluid catalytic cracking reactor to produce regenerated catalyst. The apparatus comprising: a first regenerator riser having an inlet in a lower portion thereof for regenerating a first mixture of the spent catalyst stream, a portion of regenerated catalyst and a first oxygen-containing stream by passing the first mixture therethrough and an outlet in an upper portion of the first riser for discharging a mixture of catalyst and first flue gas from the first riser; a second regenerator riser; means for separating and discharging the first mixture from the first riser and downwardly directing catalyst from the first mixture from the first riser to a first catalyst bed; means for withdrawing from the apparatus the first flue gas stream from the discharged first mixture; means for adding a second oxygen-containing stream to the first bed; means for passing a second mixture of catalyst and gases comprising the NO/sub chi/ from the first bed into the upper portion of the second riser; an enlarged catalystmore » collecting chamber above the first catalyst bed; means for discharging the second mixture from the second riser and downwardly directing the second mixture from the second riser to a second catalyst bed; means for separating a second flue gas stream from the second mixture prior to passing the second mixture into the second bed; means for adding a third oxygen-containing gas stream to the second bed; means for recycling regenerated catalyst from the second bed to the first riser; means for withdrawing regenerated catalyst from the second bed; and means for separating a third flue gas stream from an atmosphere of the collecting chamber above the second bed.« less