The time-lag of downcomer caused by the influence of volume on liquid flow and mass transfer has been ignored for establishing the dynamic model of distillation column succinctly. And there is some discrepancies with commercial column. Based on the information of a commercial ethylene column

the paper set up the mechanism model of the theoretical downcomer. In addition

the improved model is the integration of the downcomer model and equilibrium stage model. The simulations of the improved model and equilibrium stage model were achieved by gPROMS

and the differences between them were shown by the comparison of the simulation results. The differences indicated that the accuracy of dynamic model by considering the influence of downcomer. Furthermore

a controller was designed for the improved model and equilibrium stage model

and there was a difference between the control parameters. It was to say

the controller designed on the foundation of ignoring downcomer may be not suit for commercial columns. Thus

considering the influence of downcomer was significant for studying the method of distillation column modeling which was the foundation of the analysis

control and optimization for distillation column.