An apparatus for separating and stripping a gaseous mixture and a stream of particles which comprises: a reactor vessel shell having a means for receiving a mixture of cracked gases and spent catalytic solid particles via a riser cross-over conduit from a riser reactor pipe located external to said reactor vessel shell and comprising an upper dilute portion and a lower stripping bed portion, at least one separating chamber for receiving said mixture of cracked gases and spent catalytic solid particles from said cross-over conduit for separating spent catalytic particulates from the cracked gases located within said reactor vessel shell and comprising a dipleg for discharging separated catalytic particulates into said lower stripping bed portion; a stripping chamber comprising at least one inlet opening communicating with said at least one separating chamber for receiving separated cracked gases from said at least one separating chamber ; a stripper vapor inlet opening for receiving stripping gas from said stripping bed portion and a stripper conduit for evacuating vapors from said stripping chamber ; and, at least one cyclone separator for receiving vapors from said stripping chamber and comprising at least one cyclone separator dipleg having an outlet for returning separated solids to the stripping bed and a vapor evacuation conduit for discharging vapors to a gas outlet collector which communicates with a vapor outlet conduit for removing separated vapors from said reactor vessel shell ; wherein said stripping chamber is positioned centrally within said reactor vessel shell and said at least one separating chamber is positioned axially about said stripping chamber and wherein said stripping chamber ascends centrally through said at least one separating chamber from a position below to a position above said at least one separating chamber . a reactor vessel shell having a means for receiving a mixture of cracked gases and spent catalytic solid particles via a riser cross-over conduit from a riser reactor pipe located external to said reactor vessel shell and comprising an upper dilute portion and a lower stripping bed portion, at least one separating chamber for receiving said mixture of cracked gases and spent catalytic solid particles from said cross-over conduit for separating spent catalytic particulates from the cracked gases located within said reactor vessel shell and comprising a dipleg for discharging separated catalytic particulates into said lower stripping bed portion; a stripping chamber comprising at least one inlet opening communicating with said at least one separating chamber for receiving separated cracked gases from said at least one separating chamber ; a stripper vapor inlet opening for receiving stripping gas from said stripping bed portion and a stripper conduit for evacuating vapors from said stripping chamber ; and, at least one cyclone separator for receiving vapors from said stripping chamber and comprising at least one cyclone separator dipleg having an outlet for returning separated solids to the stripping bed and a vapor evacuation conduit for discharging vapors to a gas outlet collector which communicates with a vapor outlet conduit for removing separated vapors from said reactor vessel shell ; <EOS>