Use of the Riccati Equation On-Line for Adaptively Controlling a CSTS Distillation Column

A third order CSTS model for the separation dynamics of packed distillation columns is converted to a form expressed in terms of deviations of input and output from steady-state. This form has been found to be necessary for the application of the Banks' method of On-Line Riccati Control. The state-dependant coefficient matrices of the process are derived analytically in terms of the fundamental length, volatility and capacitance parameters of the process. Having successfully tested the modified model against the original, whole-value, simulation model and against analytic behavioural prediction, simulation experiments are conducted, comparing the responses and costs of the Banks' -controlled system with linear output feedback. The optimal control is found to be significantly superior to linear control for equal input excursions, in terms of cost-function-value, energy consumption and for large turn-down ratios, speed-of-response. The results offer promise for the control method when applied to tubular columns in the future.