Patent ID: 7316773

Claim:
A catalytic cracking process, which comprises: 1) catalytic cracking a feedstock in a first riser for less than about 1.5 second and sending a resultant stream into a first separating device; 2) catalytic cracking a recycle oil obtained from the first separating device in a second riser for less than about 1.5 second and sending a resultant stream into the first separating device; and 3) carrying out catalytic reaction of a crude gasoline stream and/or optionally a diesel oil stream obtained from the first separating device in a descending third riser; wherein the reaction conditions and the catalysts used in the first to third risers are selected according to the requirement for the product of the catalytic cracking process, and the catalyst regeneration and recycle systems are formed respectively for the catalysts used in the first to third risers, wherein a high temperature catalyst coming from a first regenerator ( 5 ) enters the lower part of the first riser ( 1 ) and contacts a feed oil, which vaporizes and reacts; after about 1 second, the resultant stream entering a first settler ( 4 ) to separate the coked catalyst from oil-vapor, and the coked catalyst returns to the first regenerator ( 5 ) for regeneration, thereby forming a first catalyst regeneration and recycle system; said oil-vapor enters the first separating device, said first separating device being a fractionation tower ( 9 ), for separation; wherein recycle oil and oil slurry coming from the bottom of the fractionation tower ( 9 ) enter the second riser ( 2 ) and contacts with the catalyst coming from the first regenerator ( 5 ) and reacts; after about 1 second, the resultant stream entering a first settler ( 4 ) for oil/catalyst separation, and the obtained catalyst also returning to the first regenerator ( 5 ), thereby forming a second catalyst regeneration and recycle system; said oil-vapor coming from the top of the fractionation tower ( 9 ) being separated into crude gasoline ( 15 ) and catalytic rich gas ( 18 ); the crude gasoline entering the descending third riser ( 3 ) and contacting with another high temperature catalyst coming from a catalyst buffer tank ( 7 ) and reacting; after about half a second, the resultant stream entering a second settler ( 6 ) to conduct oil/catalyst separation; the obtained catalyst entering a catalyst transfer and coke burning conduit ( 8 ) and returning to catalyst buffer tank ( 7 ) after regeneration, thereby forming a third catalyst regeneration and recycle system; wherein oil-vapor coming from the top of the second settler enters a stripping tower ( 10 ); the resultant top oil-vapor being separated into high-octane gasoline and cracked gas, the cracked gas entering an absorptive stabilization and gas separation system; wherein C4+olefins ( 16 ) obtained in the gas separation system return to the third riser ( 3 ), which contacts with the high temperature catalyst coming from catalyst buffer tank ( 7 ) and reacts.