Underflow cyclone with perforated barrel

Claim 1

In a fluidized catalytic cracking process wherein a heavy feed is catalytically cracked by contact with a regenerated cracking catalyst in a cracking reactor to produce lighter products and spent catalyst, and wherein spent catalyst is regenerated in a catalyst regeneration means containing primary and secondary separators for recovery of catalyst and fines from flue gas to produce a flue gas stream containing entrained catalyst fines, the improvement comprising use of a third stage separator to remove at least a portion of the catalyst fines from the flue gas, said third stage separator comprising: a cylindrical cyclone body having a length and a cylindrical axis; a tangential vapor inlet connective with an inlet end of said cyclone body for a stream of vapor and entrained fines; a cylindrical vapor outlet tube within said inlet end of said cylindrical cyclone body for withdrawal of gas with a reduced entrained fines content, said outlet tube having a cylindrical axis aligned with said cylindrical axis of said cyclone body; and a plurality of radially and longitudinally distributed fines outlets for removing most of said entrained fines and a minor amount of gas, comprising at least two sets of openings over at least a third of the length of said cyclone body and wherein said sets of openings are uniformly radially distributed and wherein essentially all of said gas with a reduced entrained fines content is withdrawn via said vapor outlet tube.