Optimation of Depropanizer Unit using Turbo Expander and Its Controller using Model Predictive Control

In this study, Turbo expander (TE) and Model Predictive Control (MPC) is suggested for depropanizer unit to increase propane recovery and improve control performance of the unit. The model that used in the MPC is a first order plus dead time (FOPDT), which tested the control performance using set point (SP) and disturbance change test. The measurement of the performance is the integral of the absolute error (IAE). As a result, use of TE in the depropanizer able to increase the recovery of propane of 8.44% (from 82.11% to 90.55%). The control structure of the depropanizer unit using turbo expander are pressure control for the TE (using proportional-integral control), composition control in the distillate flow (using MPC), and pressure control in depropanizer column (using MPC). The control performance after carrying out the tests show that at the SP change, the composition control and the pressure control in depropanizer unit has lower IAE values for MPC than PI contoller. Similarly when tested using disturbance rejection, the IAE of MPC is lower than PI controller. It means that MPC is better than PI controller for composition control and pressure control in depropanizer unit.