Process for the thermal cracking of heavy oils with a fluidized particulate heat carrier

In a process for the thermal cracking of heavy oils with a fluidized bed of a particulate heat carrier wherein (a) a fluidized bed of the particulate heat carrier is formed in a reactor by fluidization with fluids comprising a heavy oil feed and steam;

• (b) said heavy oil is thermally cracked at a temperature of 700.degree. to 850.degree. C. to form a cracked oil product;
• (c) the cracked oil product together with particulate heat carrier escaping from the reactor is passed through a cyclone to remove a major portion of the particulate heat carrier therefrom;
• (d) the particulate heat carrier removed from the cracked oil product in the cyclone is returned to the reactor;
• (e) the cracked oil product containing the remaining portion of said particulate heat carrier is quenched to provide a cracked oil having the remaining particulate heat carrier suspended therein;
• and (f) said cracked oil is fractionated to provide a relatively high boiling oil containing the particles of the heat carrier suspended therein;
• the improvement comprising:
• locating the cyclone for separating the particulate heat carrier from the cracked oil product outside the reactor;
• returning the portion of the particulate heat carrier removed in the cyclone to the reactor at a position which is below the position where said heavy oil is fed into the reactor;
• separating said high boiling oil and said remaining portion of particulate heat carrier in a gravitational separator wherein the high boiling oil is separated into two portions, one containing relatively coarse particles of the particulate heat carrier densely suspended therein and the other containing relatively fine particles of the particulate heat carrier suspended therein, and returning said relatively coarse particles of the particulate heat carrier to said fluidized bed.