Simulation And Optimization Of The Gas Fractionation Unit In The RFCC

Many problems exist in the gas fractionation unit of the DaQing Petrochemcal Company Refinery, such as high reflux ratio, high operating pressure, wide range of pressure variety and excessive purity of product. The practical energy-consumed is 4367.67MJ/t. It is higher 8.3% than the design energy-consumed and the energy-consumed expense will increase 3.360 billion Yuan per year. This gas fractionation unit exist the larger potential of saving energy by adjusting the operation comditions. On the basis of the simulation results by Aspen Plus, a petrochemical flowsheeting simulation software, the operation parameters such as pressures, temperature, reflux ratio and purity of products which can influence energy-consumed of the gas fractionation unit have been extensively studied in this thesis. The optimal parameters and optimizing approach of the gas fractionation unit operation are obtained.The main adjustment purpose of the gas fractionation unit operation is quality optimize control, and control target is 99.60±0.05%(wt) above the assurance of the propylene purity≥99.50%(wt). When the reflux ratio of the propylene tower is lower to 14.30 from 16 and the propylene purity is lower to 99.60%(wt) from 99.80%(wt), the thermal load will be reduce 9.73GJ/h. It is good for controlling the depropanization tower, deethanization tower and propylene tower. These three towers should be operated in lower-pressur to the greatest extent, but the operation pressures should not be lower than 1.59MPa,1.79 MPa and 1.62 Mpa, respectively. The thermal load of the propylene tower is more than 70% of the total unit's. In fact, we should pay attention to the pressures control and optimization of the propylene tower in the factual operation .The lower pressures operation should be adopted possibility under the assurance of the propylene purity≥99.50%(wt). By following the tracks of the propylene and propane component of the propylene tower's feed, a table reflecting the relationship between the component and matchable reflux ratio is obtained. Under the assurance of the propylene purity≥99.50%(wt), the operators can adjust the reflux ratio of the propylene tower by this table easily.Now, the conclusion and simulation result of this reaserch have be adopted. The propylene purity controls at 99.60±0.05%(wt), and the energy-consumed of the gas fractionation unit controls at 4063.78GJ/h which has reached the design level. The energy-consumed belong to the lower level in the same type domestic unit.