Analysis of the Transfer Function Model of Tray-Type Binary Distillation Columns with Liquid Hydraulic Delay

摘要

A transfer function model (TFM) in the frequency domain is used to predict that a distillation column system (compositions to terminal flow rate) is a low pass filter with large time constants and low cut-off frequency. Computed results in frequency and time domains reveal the strong resemblance of the dynamic behavior of this system to that of first order lag, both qualitatively and quantitatively. At low frequency the elements of the TFM can be expanded by Taylor theorem into an approximate analytical model of a first-order-lag type. Solving difference equations directly can give more exact results, so that the better way to describe a tray-type distillation column in frequency domain is to use difference equations. There is no need to use differential equations to approximate the difference equation.