Absorber-Stripper-Stabilizer System in FCCU to Decrease Gasoline Product Olefin Content and Improve Propylene Yield

Based on technical characteristics of two-stage riser for maximizing propylene (TMP) technology in fluidiged catalytic cracking unit (FCCU), light/heavy gasoline separator was set in the absorber-stripper-stabilizer system to have light gasoline distilled from the stabilized gasoline re-cracked in the second stage riser to decrease gasoline product olefin content and maximize unit propylene yield. Considering the industrial data from the original pilot unit of one refinery in China, further research was carried out on the new process using the process simulating method to optimize process operating conditions. Field data from the optimized industrial pilot unit showed that gasoline product olefin content decreased from more than 50% to less than 35%, meeting China environmental standards Ⅱ. The propylene yield was 21.28%, 1.64% higher than that of the primary design. Stabilized gasoline stream from the stabilizer bottom served as heat source for the bottom reboiler of the new light/heavy gasoline separator. Therefore, energy consumption of the new process was not increased and system residual heat utilization ratio was improved. Conclusions are drawn that the new process proposed can optimize components of light gasoline remarkably that is re-cracked in the second stage riser in TMP technology, and thus can improve unit propylene yield, decrease gasoline product olefin content effectively, without increasing unit energy consumption.