Dynamics and control of high-purity distillation systems

A new control structure for high-purity distillation columns is developed. It is shown that the slow nonlinear transients characteristic of such columns can be effectively damped by independent manipulation of the internal reflux-ratios (;An Internal Reflux-Ratio (IR) control scheme is proposed for high-purity binary columns. It is based on feedback control of the impurity concentration leaving each end of the column by independent manipulation of the corresponding internal reflux-ratio. The performance of such (IR) control is compared against feedback control based on the manipulation of column reflux and vapor boilup (LV Control) and against feedback control based on independent manipulation of the external flow ratios at each end of the column (;IR control schemes are also proposed for three thermally coupled distillation networks for high-purity separation of ternary mixtures: (1) Thermally Coupled System with Stripping Column (TCS-S), (2) Thermally Coupled System with Rectifying Column (TCS-R) and (3) Petlyuk Column (TCS). Excellent on-aim regulation of the product stream impurity compositions for these three distillation networks is demonstrated.