A Case-Study of Multivariable Control for a Multicomponent Distillation Unit on a Pilot Plant Scale

Robust multivariable control strategies based on H¿-minimization are developed for a pilot plant distillation unit consisting of two coupled distillation columns for the separation of the mixture Methanol/Ethanol/n-Propanol. A comparison is made between several control strategies in nonlinear simulation and experiment. Controller design is based on transfer function matrices describing column dynamics in the vicinty of the operating point. The controllers are designed to keep product specifications by plate temperature control. The problem of choosing appropriate locations for temperature measurements is also addressed. Constraints on the manipulated variables have to be considered in the design. Qualitative physical intuition is used for selecting appropriate weighing functions.