Controlling III-conditioned plants: SISO controllers in distillation

Singular Value Decomposition is applied to compare performance of different control schemes for distillation columns, for which SISO controller structures have been adopted to reduce sensitivity to uncertainty in the manipulated variables. The steady state analysis, based on a linear model of the process, predicts better performance for the D-V scheme (using Distillate and Vapour). Simulation, carried out via a detailed non-linear model, shows that the L-V control scheme (using Reflux and Vapour) can give acceptable performance for the rejection of feed disturbances. Analyzing different operating conditions, the L-V scheme is found to give inferior results for disturbances in feed flow rate, when the feed is partly vapour.