Abstract: A process of thermally cracking a heavy petroleum oil wherein the heavy petroleum oil is treated successively in a cracking furnace and then in a perfect mixing type tank reactor. The thermal cracking in the cracking furnace is performed at a temperature at the outlet of the cracking furnace of 450.degree.-520.degree. C. with a conversion of at least 60-75% of the overall conversion rate while the thermal cracking in the tank reactor is performed at a temperature of 400.degree.-450.degree. C. a pressure of from ambient pressure to 1 kg/cm.sup.2 for a period of time of less than 30 minutes but not less than 10 minutes while feeding steam having a temperature of 435.degree.-700.degree. C. to the tank reactor in an amount of 8-20% by weight of the heavy petroleum oil fed to the cracking furnace.

Abstract: A process for the thermal cracking of heavy oils with a fluidized particulate heat carrier is carried out while recovering particles of the heat carrier accompanied by a stream of the reaction product by means of a cyclone and a gravitational separator, returning the particles of the heat carrier recovered by the cyclone directly to the reactor and returning the particles of the heat carrier recovered by the gravitational separator to the reactor in the form of suspension in a cracked oil.