Catalytic cracking system

In a fluidized catalytic hydrocarbon cracking process wherein hydrocarbon conversion is carried out in a downflow transport type reaction zone in the presence of hot freshly regenerated catalyst, spent catalyst from said reaction zone is separated from reaction products and stripped of volatile hydrocarbons in a fluidized bed catalyst stripping zone, stripped catalyst is regenerated with an oxygen-containing gas in a catalyst regeneration zone, and hot freshly regenerated fluid catalytic cracking catalyst from the regeneration zone is supplied by gravity in the absence of a carrier fluid into the upper end of a vertical transport downflow reaction zone of relatively small cross-sectional area as compared with its length the improvement which comprises discharging reaction products and catalyst from said reaction zone axially downward directly into the upper portion of an unobstructed ballistic separation zone having a cross-sectional area within the range of 20 to 30 times the cross-sectional area of said reaction zone and open at its lower end to said stripping zone thereby permitting unobstructed free fall of catalyst under the influence of gravity from said reaction zone through said separation zone directly into said stripping zone, introducing hydrocarbon feedstock into said reaction zone along the path of flow of said catalyst forming a mixture consisting of regenerated cracking catalyst and hydrocarbon feedstock vapors at an elevated temperature in the range of 900.degree. F. to 1100.degree. F., maintaining contact between catalyst and hydrocarbon reactants in said reaction zone for an average contact time in the range of 0.5 to 5 seconds, maintaining a fluidized bed level in said stripping zone well below the discharge end of said reaction zone, and effecting substantially complete separation of spent catalyst from hydrocarbon conversion products in said separation zone solely by particle inertia and gravity, withdrawing hydrocarbon conversion products separated from said catalyst in said separation zone at substantially the level of discharge from said reaction zone such that said products are drawn horizontally outward away from the downwardly moving catalyst particles in said separation zone, and collecting separated catalyst from said ballistic separation zone in a fluidized bed in said stripping zone.