Process Simulation For Propylene Rectification Tower

The process of propylene rectification tower was simulated in stable-state and dynamic simulation with Aspen Plus and Aspen Dynamics.The high efficiency and large throughput of DJ type plates were verified by comparing the simulateion results with practical operating results.The simulation value of flooding modulus was modified reasonably by 76% using the contrast results between simulation results and design data.A new way of process simulation with common plates instead of DJ type was created accordingly.It was found that the number of theoretical plates was 128,more than designed number of 118 for reconstruction,which indicated that the main reason failed the reconstruction for the first time was the lack of plates due to estimated less of designed theoretical number of plates.Reasonable optimum simulation process were:confirmation of simulation input initial value―best feed inlet―best reflux ratio― best yield range― other optimized parameters.The optimized adjusting rules for propylene rectification tower were summarized as following:with the same composition but increased amount of feed, the best reflux ratio and feed inlet kept unchanged, and the yield of column went up, the adjusting range of yield expanded respectively,the load of overhead condenser and column reboiler raised,the temperature of column stabilized and the flooding modulus added too;with the same amount of feed but increased content of propane,the number of plates in the best feed inlet,the best reflux ratio and the yield of column increased respectively,and the adjusting range of yield expanded,load of overhead condenser and column reboiler raised,column temperature down and flooding modulus up.Followed with optimized process,the concentration of propylene overhead kept at 99.63% to 99.65%,and the concentration in column pot lied from 5.43% to 7.92%.Exchanging the two towers position was beneficial to process under large amount.Dynamics properties showed that the amount or composition of feed,or quantity of reflux disturbance all had relatively great impact on the process,which mainly reflected on the fluctuation of 406 tower pot temperature,condenser and reboiler load,concentration of propylene over and in the column,the yield over and in the column which not only fluctuated greatly,but responded rapidly.The concentration of propylene over and in the column responded slowly and the fluctuating period exceeded 3 hours.These dynamic properties required steady and gradual operation and adjustment.The adjusting rules for instruments impacted the dynamics properties greatly.