Abstract: Since the recovery rate of propylene in gas fractionation unit was usually less than 95%, a simulation of the whole processing scheme for a 0.2 Mt/a gas fractionation unit was carried out using PRO/II software to study the causes of propylene loss and the countermeasures. Feeds with various compositions including design value were used in simulation and the reliability of simulation was validated. Results showed that the loss of propylene mainly came from the top outlet gas of deethanizer and the bottoms of propylene fractionating tower, in which the former occupied more than 65% of the total propylene loss. Feasibility study of eliminating deethanizer and using dual-tower process was carried out. It was found that if the mol content of C2 in feed could be controlled to less than 0.10%, the dual-tower process could be realized. Simulation data showed that with the adoption of dual-tower process and optimizing the operation conditions of propylene fractionating tower, the recovery rate of propylene in gas fractionation unit could reach more than 99%.

Key words: gas fractionation unit, process simulation, propylene, deethanizer