Shih-Bo Hung

Control of reactive distillation columns for amyl acetate production using dilute acetic acid

Abstract This work explores the feasibility of recovery of acetic acid from aqueous solutions with different acid concentrations. Instead of separating acid from water using azeotropic distillation, acetic acid is converted to acetate via esterification. A range of acetic acid concentrations is explored, varying from 100 wt%, to 75 wt%, to 50 wt%, and then to 30 wt%. The Total Annual Cost (TAC) analysis shows that a standalone reactive distillation is more economical than a flowsheet with a pre‐treatment unit. Process characteristics have been explored and the results show significant nonlinearity associated with reactive distillation columns for all four different acid concentrations. A systematic design procedure is devised to control reactive distillation columns by temperature control. Reasonable control performance can be achieved. A further improvement can be made by incorporating feedforward control for feed flow disturbance. Finally, one‐temperature‐one composition control structure is also examined. Acceptable control performance can be obtained while maintaining acetate composition.

Dynamics and Control of Reactive Distillation Configurations for Acetic Acid Esterification

Abstract Three different flowsheets have been proposed for acetic acid esterification of acetic acid with alcohols ranging from C 1 to C 5 according to the ranking of normal boiling points and immiscibility. This work explores the similarities and differences in the dynamics and control of these three types of flowsheets. The degree of process nonlinearity can be computed quantitatively based on the fraction of “sign reversal” for all tray temperatures or based on Allgowers nonlinearity measure. These measures provide useful information to the potential problems in closed-loop control. Next, a systematic design procedure is proposed to devise control structures for all three types of flowsheets for these five esterification systems. The simulation results reveal that reasonable control can be achieved for all five systems with different degrees of asymmetry in closed-loop responses as predicted by the nonlinearity measures. Simulation results clearly show that the simple decentralized control provides a workable solution for highly nonlinear reactive distillation columns under various flowsheet configurations.

A Smith Predictor Enhanced PID Controller

Abstract In this work, a Smith predictor enhanced PID controller, SP-PID, is proposed. A tuning parameter Kspis devised which gradually transforms the controller from a PID controller toa Smith predictor as Ksp changes 0 to 1. Properties of the SP-PID are explored and design procedure is given to ensure a certain degree of robustness. Simulation results clearly indicate that the SP-PID takes advantage of the SP when small modeling error is encountered and it is gradually detuned to a PID controller, a user friendly controller, when the model quality degrades. Moreover, the proposed concept can be implemented to current process control computer with virtually no extra hardware cost.