Two stage fluid catalytic cracking process and apparatus

A process for two stage fluid catalytic cracking (FCC) of hydrocarbon feedstocks boiling above 200° C. for simultaneous maximization of light olefins and middle distillate range hydrocarbons with flexibility of alternate mode of operation for the maximization of gasoline by carrying out the cracking operation in two separate flow reactors operating under varying severities using different and independent catalyst systems with simultaneous regeneration of respective catalysts comprising the following steps:

• (a) contacting fresh hydrocarbon feedstock with regenerated catalyst of first type at a catalyst/oil ratio of 4-15;
• wherein the catalyst of the first type is an intermediate pore size zeolite catalyst selected from the types Y, REY, USY and RE-USY under fluidized condition in presence of steam in a first flow reactor for cracking of the hydrocarbon at a lower temperature and for a short contact period, wherein a residence time of hydrocarbon is kept between 0.5-2 seconds, to produce a mixture of spent catalyst and reactor effluent vapors,
• (b) separating the spent catalyst of first type from the reactor effluent vapors of step (a) quickly using a fast gas solid separator, the separated spent catalyst of the first type being subjected to multistage steam stripping to remove the entrapped hydrocarbon vapors followed by regenerating the spent catalyst of the first type in an up flow catalyst regenerator using air/oxygen containing gas to obtain a regenerated catalyst of first type with carbon content below 0.1 wt % suitable for the cracking operation again in the first flow reactor,
• (c) separating the first reactor effluent vapors of step (a) using a first separator/fractionator into three fractions which are hydrocarbons boiling below 150° C., liquid hydrocarbons with boiling range 150-370° C. and unconverted bottoms (370° C.+) and sending the hydrocarbons boiling below 150° C. to a second product separation section for further separation into products of different desired boiling ranges and liquid hydrocarbons with boiling range 150-370° C. is directly blended with similar cuts obtained from the second product separation section,
• (d) contacting the unconverted bottoms (370° C.+) from first fractionator, whole or a part of hydrocarbons in the boiling range of naphtha and C4 hydrocarbons from the second product separation section with regenerated catalyst of second type, wherein the catalyst of the second type consists of a mixture of large pore bottom selective active material of pore size more than 50 Angstroms and shape selective pentasil zeolite based catalyst in a second flow reactor at a catalyst/oil ratio of 13-25, at higher severity than the first flow reactor at a higher temperature and higher contact period under fluidized condition in presence of steam to produce a mixture of spent catalyst of second type with reactor effluent vapors,
• (e) separating the spent catalyst of second type from the reactor effluent vapors of step (d) quickly using a fast gas solid separation device, and steam stripping with a counter current steam flow followed by regeneration of the spent catalyst of second type in a dense bed/fast fluidized bed regenerator with air/oxygen containing gases to obtain the regenerated catalyst of second type with carbon content below 0.1 wt % suitable for the cracking operation again in the said second flow reactor, and
• (f) separating the reactor effluent vapors from the second stage flow reactor into fuel gas containing inerts, hydrogen sulphide, hydrogen, methane and ethane, ethylene, C3 hydrocarbons (propane, propylene), C4 hydrocarbons and liquid products according to the desired boiling ranges, in the second product separation section.