Image Number 2 for United States Patent #4875994.
A process and apparatus for cracking heavy hydrocarbons using a mixture of fluid cracking catalyst and a demetallizing additive differing in physical characteristics from the cracking catalyst is described. A heavy, metals containing feed such as a resid contacts demetallizing additive in the base of a riser reactor. The demetallized resid is cracked by contact with a stream of hot, regenerated catalyst. A mixture of metal containing additive, deactivated cracking catalyst, and cracked products is discharged from the riser. The metal containing additive and deactivated catalyst are stripped, preferably with steam, and charged to a two-stage regenerator. The first stage of the regenerator partially regenerates the cracking catalyst and separates it by elutriation from the demetallizing additive, which accumulates as a dense phase fluidized bed in a lower portion of the first stage regenerator. Partially regenerated cracking catalyst is carried up out of the first stage regenerator and regeneration is completed in a second stage regenerator by contact with an oxygen containing gas. Demetallizing additive is withdrawn from the first stage of the regenerator and charged to the base of the riser. Hot regenerated cracking catalyst is withdrawn from the second stage regenerator and recycled to the riser. Preferably, heat removal means are provided in the first or second stage regenerator, the additive return line, or the regenerated catalyst return line to the riser. An additional stripping stage, preferably a hot stripper operating with CO as a stripping gas, may be provided intermediate the conventional stripping section and the regenerator.