PAIRING AND LOOP TUNING OF A TRAY DISTILLATION COLUMN

A control strategy was developed to determine the appropriate control loops that let the column to operate at steady state without flooding, weeping and entrainment. The aim is to operate the column with the required top and bottom compositions. From the control strategy, block diagrams were constructed and the transfer functions were identified. From these block diagrams the overall transfer functions were calculated and the characteristic equations were obtained, both for closed and open loops. The characteristic equations were then used for stability analysis, tuning, offset investigation and response simulation. As these multi-loops are interactive, pairings for the controlled and manipulated variables were determined using relative gain array (RGA) and the loops were coupled according to the magnitude of the interaction indexes.