Control of different reactive distillation configurations

Three different flowsheets have been proposed for acetic acid esterification of acetic acid with alcohols ranging from C1 to C5 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 is analyzed qualitatively based on the residue curve map and the boiling point ranking and it can be computed quantitatively based on the fraction of "sign reversal" for all tray temperatures or based on Allgower's 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. Dual-temperature control and one-temperature/one-composition control are studied. Simulation results clearly show that the simple decentralized control provides a workable solution for highly nonlinear reactive distillation columns under various flowsheet configurations. (c) 2005 American Institute of Chemical Engineers