Multivariable control of a binary distillation column

This work compares the performance of several multivariable control strategies on the control of a simple binary distillation column. The study is based on a detailed nonlinear simulation of a 20 tray n-octane/n-pentane column.

An extensive analysis of the column was conducted to find its steady-state gains and to fit more sophisticated models (first order lag, second order lag) to it. The distillate and bottoms compositions were controlled by manipulating the distillate flowrate and the steam rate to the reboiler. A relative gain analysis was done to determine the best way to pair controller loops in a non-decoupled scheme. A v-canonical decoupler and the different types of p-canonical decouplers were added and any improvement in response noted. Various degrees of decoupler element sophistication (steady-state, lead-lag, etc) were also examined. New-variable techniques were investigated, and steady-state singular value decomposition was used in a more advanced control scheme. Finally, the results were discussed and compared to highlight the advantages and disadvantages of each control method.