Abstract:  Taking the absorption-stabilization sections in three FCC units as example, this paper uses Aspen plus to simulate the different theoretical plate positions of crude gasoline to the absorbing tower of FCC units. With similar C₃ and C₄ concentrations at the top of absorbing towers and with the constraints of minimum consumption of supplementary absorbent and minimum energy consumption (heat load and cooling load of reboiler) in the absorption-stabilization section, the three units have different propylene yields, different pressures of the oil and gas separators at the top of distillation towers and different propylene contents of crude gasoline. The results show that the optimum feed position of the crude gasoline to absorbing tower is jointly affected by the pressure of oil and gas separator at the top of distillation tower and the propylene content of crude gasoline. The higher the pressure is, the lower the feed position is, and this has nothing to do with the propylene yield. The higher the propylene content of crude gasoline is, the lower the optimum feed position of crude gasoline to absorbing tower is.

Key words: fluid catalytic cracking/FCC, absorbing tower, crude gasoline, feed position