Multi stage selective catalytic cracking process and a system for producing high yield of middle distillate products from heavy hydrocarbon feedstocks

A fluidized bed catalytic cracking system, for the production of high yield of middle distillate products comprising hydrocarbons having carbon atoms in the range of C8 to C24 from heavy petroleum feeds, comprising:

• A. at least two riser reactors (1 and 2) means to introduce a fresh feed into the first riser reactor (1);
• B. mean at the end of the first riser reactor (1), to quickly separate the spent catalyst from hydrocarbon product vapors;
• C. means to steam strip said spent catalyst under conditions sufficient to remove entrained hydrocarbons;
• D. first conduit means (5), adapted to:
• feed a part of the said stripped catalyst into a regenerating apparatus (7), and feed another part of the stripped catalyst into a mixing vessel (10);
• E. second conduit means (19) adapted to feed mixed catalyst to a point proximate to the bottom of the first riser reactor (1)
• F. third conduit means (12) adapted to feed hydrocarbon product vapors separated from the catalyst evolved from said first riser reactor to a distillation column (13);
• G. means to separate first cracked hydrocarbon products into a first fraction comprising hydrocarbons having boiling points not greater than about 370° C. and a second fraction comprising hydrocarbons with boiling points not less than about 370° C., including uncracked feed fractions;
• H. fed nozzle means (16) to feed said second fraction, comprising uncracked hydrocarbon products, into the bottom of said second riser reactor (2) at a point above the regenerated catalyst entry zone;
• I. means to feed regenerated catalyst from the regenerating apparatus (7) to the bottom of the second riser reactor (2) through a conduit (9);
• J. means to separate the hydrocarbon products of the second riser reactor (2) from the spent catalyst;
• K. means to separate the cracked products of the second riser reactor (2), along with the products of the first fraction of the first riser reactor (1) comprising hydrocarbons, with boiling points not greater than about 370° C. into fractions comprising dry gas, LPG, gasoline, heavy naphtha, light cycle oil, heavy cycle oil, and slurry oil;
• L. means, including a separate feed nozzle (17) located at a point lower than the position of introduction of main feed, to recycle substantially all of the heavy cycle oil and at least part of the slurry oil, comprising hydrocarbons with boiling points of at least about 370° C., to said second riser reactor (2);
• M. means to pass the feed and cracked product vapors together with said catalyst, into the second riser;
• N. means to separate spent catalyst from product vapors of the second riser reactor (2);
• O. means to strip entrained hydrocarbons from spent catalyst;
• P. means to conduct stripped catalyst through a conduit (18) into the regenerating apparatus (7);
• Q. means to regenerate said stripped catalyst and to produce a hot regenerated catalyst;
• R. means to separate said hot regenerated catalyst into two parts, means to pass one part of said hot regenerated catalyst to the mixing vessel (10) through a conduit (8) and means to pass the other part of said hot regenerated catalyst directly to the bottom of the second riser reactor (2);
• S. means to pass the mixed catalyst from the mixing vessel (10) through a conduit (19) to the inlet of the first riser reactor (1);
• T. means to control:
• the catalyst bed level in said stripping means, the catalyst circulation rate from the common regenerator, and
• the quantity of the spent and regenerated catalyst entering into the mixing vessel (10) using slide valves placed in said conduits;
• and
• thereby producing a high yield of middle distillate products.