Fluid catalytic cracking with plurality of catalyst stripping zones

A method of fluid catalytically cracking a hydrocarbon feed with a catalyst in a riser conversion zone and subsequently regenerating catalyst recovered from said riser conversion zone to heat said catalyst to remove carbonaceous deposits before returning to said riser conversion zone, comprising:

• (a) introducing hydrocarbon feed and catalyst into an upstream end of a riser conversion zone to yield a gasiform mixture of catalyst and cracked hydrocarbons exiting a downstream end of said riser conversion zone, said riser conversion zone comprising a vertically elongate tubular conduit;
• (b) deflecting catalyst in said mixture exiting said downstream end of said riser conversion zone downwardly to a primary stripping zone to separate a portion of said catalyst from said cracked hydrocarbons;
• (c) contacting said downwardly deflected catalyst with a stripping medium introduced into said primary stripping zone to separate said downwardly deflected catalyst from hydrocarbons and form a first stream of stripping gas and stripped hydrocarbons;
• (d) separating in a cyclone separator a portion of said catalyst which was not deflected downwardly in step (b) from said cracked hydrocarbons;
• (e) introducing stripped catalyst from said primary stripping zone and catalyst from a dipleg of said cyclone separator directly into a secondary stripping zone;
• (f) passing stripped catalyst from said secondary stripping zone directly into a first stage regenerator;
• (g) introducing regenerated catalyst output from said first stage regenerator into a second stage regenerator;
• and
• (h) recycling hot regenerated catalyst from said second stage regenerator directly into said secondary stripping zone to maintain the secondary stripping zone at a temperature above that of the stripped catalyst from the primary stripping zone and to form a second stream of secondary stripping gas and stripped hydrocarbons removed from the catalyst in the secondary stripping zone,
• (i) combining the first and second streams of stripping gas and stripped hydrocarbons outside the primary stripping zone.

A process for fluid catalytic cracking of a feedstock containing hydrocarbons, comprising the steps of:

• passing a mixture comprising catalyst and said feedstock upwardly through a riser conversion zone under fluid catalytic cracking conditions to crack said feedstock, said riser terminating in a reactor vessel;
• discharging said mixture, having a discharge temperature between 900.degree. and 1100.degree. F., from said riser;
• cyclonically separating a first portion of catalyst from said mixture in a centrifugal separator, with a remainder of said mixture forming a separator gaseous effluent stream, immediately passing said first portion of separated catalyst from said centrifugal separator to a preliminary stripping zone, said preliminary stripping zone being defined by a preliminary stripping vessel attached to said centrifugal separator and located below said centrifugal separator, said preliminary stripping vessel having an entrance, a catalyst exit, and an exit for passing stripped hydrocarbons through said centrifugal separator;
• non-cyclonically stripping said first separated catalyst by injecting a first stripping gas into said preliminary stripping vessel at an injection location for exposure to a portion of said first portion of separated catalyst located above said injection location after said first portion of separated catalyst has been centrifugally separated from said gaseous effluent stream;
• passing said first stripping gas, and hydrocarbons stripped from said separated catalyst, directly to said stripped hydrocarbon exit as said separator gaseous effluent stream without contacting a remainder of said first portion of separated catalyst;
• heating said separated catalyst portion by combining said first separated catalyst portion with a first portion of regenerated catalyst from a fluid catalytic cracking regenerator vessel to form combined catalyst;
• gravity feeding said first portion of regenerated catalyst into a hot stripping zone;
• hot stripping said combined catalyst by contact with a second stripping gas stream, in said hot stripping zone to form a hot stripped catalyst stream and a hot stripper gaseous stream, at a hot stripping temperature between 100.degree. F. above said discharge temperature and 1500.degree. F., said first regenerated catalyst portion having a temperature between 100.degree. F. above said hot stripping temperature and 1600.degree. F. prior to heating said separated catalyst, wherein said hot stripper gaseous stream has a residence time of 0.5 to 10 seconds in said hot stripping zone;
• and
• regenerating said hot stripped catalyst in a fluid catalytic cracking regenerator vessel by contact with an oxygen-containing stream at fluid catalytic cracking regeneration conditions, comprising a temperature in the range from 100.degree. F. above that of said hot stripping temperature to 1600.degree. F.