Abstract: Aspen Plus process simulation software based on SRK thermodynamic equation- physical properties of the BM algorithm and RadFrac rectification tower module was used to simulate and optimize a 600 kt/a gas separation unit in PetroChina Sichuan Petrochemical Co. Ltd. The software was to improve the efficiency of the plate, and to simulate the influence on the quality of the product from depropanizer and propylene rectification tower, including the optimization of the bottom temperature, the parameters of reflux and the feed plate. The results showed that the feed mainly composed of propylene and propane had little difference with the result of simulation, leading to an increasing on yield of propylene by 0.43 percentage point, when the temperature at the bottom of the depropanizer tower was (103.8±0.1) ℃, the flow rate at the top was (95±5) t/h, and the feed plate kept the 29th layer. The purity of propylene was increased by 0.07 percentage point when the feed temperature of the column was 40.3 ℃, the bottom temperature of the column was 54.8 ℃, the top flow rate was 357 t/h, and the feed plate position was changed to the 136th layer. During optimization process, heat saving at the bottom of the tower reduced the operation cost of the unit by about 9.045 million CNY/a. The production of propylene and the economic benefits were increased by about 2117.39 t/a and about 15.245 million CNY/a, respectively.

Key words: gas fractionation, thermodynamic equation, simulation optimization, propylene rectification, depropanizer