(189d) Dynamics and Control of Reactive Distillation Column with External Recycle | AIChE

(189d) Dynamics and Control of Reactive Distillation Column with External Recycle

Authors 

Chen, H. - Presenter, Beijing University of Chemical Technology
Reactive distillation columns with external recycle between the top and bottom (RDCs-TBER) have a better steady-state performance as compared with conventional reactive distillation columns (CRDCs) for the separations of reacting mixtures featuring the most unfavorable ranking of relative volatilities (i.e., the reactants are the lightest and heaviest components with the generated products in between). In this article, their dynamics and control are studied in great detail, with special attention given to the influences of external recycle on process dynamics and controllability. Three kinds of control systems are developed. The top and bottom levels of all control systems are controlled by reflux flow rate and reboiler heat duty, respectively. The only distinguish of these three control systems is that one is with constant external recycle, another is with constant reflux ratio, and the last is controlling the product purity with external recycle flow rate.

Two reactive distillation systems, executing a hypothetical reversible reaction, A + B ↔ C + D (αA > αC > αD > αB), and lactic acid esterification, are employed to inspect the dynamics and controllability of the RDC-TBER. The results show that the supplementary manipulated variable (i.e., the flow rate of the external recycle) can be used to improve the process operation. The RDC-TBER, on the other hand, shows greatly improved tracking performance with even enhanced disturbance rejection capabilities.