Catalytic cracking process and apparatus with refluxed spent catalyst stripper

A fluidized catalytic cracking process wherein a heavy hydrocarbon feed comprising hydrocarbons having a boiling point above about 650.degree. F. is catalytically cracked to lighter products comprising the steps of:

• a. catalytically cracking said feed in a catalytic cracking reactor operating at catalytic cracking conditions including a cracking temperature of 425.degree. to 600.degree. C. by contacting said feed with a source of regenerated catalyst to produce a cracking reactor effluent mixture comprising cracked products and spent cracking catalyst containing coke and strippable hydrocarbons;
• b. separating said cracking reactor effluent mixture into a cracked product rich vapor phase and a solids rich phase comprising said spent catalyst and strippable hydrocarbons;
• c. heating said solids rich phase by mixing it with a source of regenerated catalyst having a temperature of 593.degree. to 871.degree. C. to produce a heated catalyst mixture comprising spent and regenerated catalyst;
• d. stripping said heated catalyst mixture and a stream of recycled, stripped catalyst with a stripping gas to remove strippable compounds from spent catalyst, in a primary counter-current catalyst stripper having:
• an upper portion with an inlet for said heated catalyst mixture and a vapor outlet for stripped hydrocarbons and stripping gas;
• and
• a lower portion having an inlet for stripping gas, and an outlet for discharge of stripped catalyst,
• to produce stripped catalyst which is discharged from said lower portion of said primary catalyst stripper;
• e. passing from 10 to 90% of catalyst discharged down from said primary stripping stage to a catalyst regeneration means;
• f. passing the remainder of catalyst discharged down from said primary stripping stage to a secondary stripping stage;
• g. stripping and cooling said remaining catalyst in said secondary stripping stage by fluidizing with a stripping gas and removing heat by indirect heat exchange with a heat exchange means having a heat transfer coefficient and wherein the heat transfer coefficient for indirect heat exchange is higher than a heat transfer coefficient across said indirect heat exchange means obtainable without the presence of added stripping gas in said secondary stripping stage, to produce cooled, stripped catalyst with a reduced content of strippable hydrocarbons and a secondary stripping vapor stream;
• h. recycling said cooled, stripped catalyst mixture from said secondary stripping zone to said inlet in said upper portion of said primary stripping zone;
• i. regenerating said cooled, stripped catalyst mixture by contact with oxygen or an oxygen containing gas in said regeneration means to produce regenerated catalyst having a temperature of 593.degree. to 871.degree. C. as a result of combustion of coke on said spent catalyst;
• j. recycling to the cracking reactor regenerated catalyst to crack more hydrocarbon feed;
• and
• k. recycling to the primary stripping stage regenerated catalyst to heat spent catalyst and wherein the weight ratio of regenerated to spent catalyst is from 1:20 to 5:1.

An apparatus for the fluidized catalytic cracking of a heavy hydrocarbon feed comprising hydrocarbons having a boiling point above about 650.degree. F. to lighter products by contact said feed with catalytic cracking catalyst comprising:

• a. a catalytic cracking reactor means having an inlet connective with said feed and with a source of regenerated catalyst and having an outlet for discharging a cracking reactor effluent mixture comprising cracked products and spent cracking catalyst containing coke and strippable hydrocarbons;
• b. a separation means connective with said reactor outlet for separating said cracking reactor effluent mixture into a cracked product rich vapor phase and a solids rich phase comprising said spent catalyst and strippable hydrocarbons;
• c. a primary stripping means adapted to contain a relatively dense phase fluidized bed of catalyst beneath a dilute vapor phase in a primary stripping vessel comprising in an upper portion thereof an inlet for a source of regenerated cracking catalyst, an inlet for spent catalyst, and a vapor outlet for stripped hydrocarbons and stripping gas and in a lower portion thereof an inlet for a primary stripping gas and an outlet for discharge of stripped solids;
• d. a secondary stripping means comprising a vessel adapted to contain a fluidized bed of catalyst and having in a lower portion thereof an inlet for stripped solids connective with said solids outlet of said primary stripping means, and an inlet for a secondary stripping gas, an indirect heat exchange means within said secondary stripping vessel for removal of heat, and at least one outlet in an upper portion of said secondary stripping means for discharge of stripped catalyst and stripped hydrocarbons and secondary stripping gas;
• and having means for refluxing stripped catalyst from said secondary stripper to said upper portion of primary stripper;
• e. a catalyst regeneration means having an inlet connective with a catalyst outlet from at least one of said primary and said secondary stripping means, a regeneration gas inlet, a flue gas outlet, and an outlet for removal of regenerated catalyst;
• and
• f. a regenerated catalyst recycle means connective with said catalyst regeneration means, with said catalytic cracking reactor inlet and with said upper portion of said primary stripping zone.