Dynamics And Control Of Totally Refluxed Reactive Distillation Columns

Economic and environmental considerations have encouragedindustry to focus on technologies based on process intensification.Reactive distillation is an excellent example of process intensification. Itcombines reactive operation and separation into one single vessel,therefore provides an economically and environmentally attractivealternative to conventional multiunit flowsheets in some systems. Withthese inherent advantages, reactive distillation becomes one of the mostimportant research branches in process intensification.According to the mechanism of the reaction operation involved,reactive distillation columns can be classify into three categories, e.g.,conventional two-end reactive distillation column, totally refluxedreactive distillation column and totally reboiled reactive distillationcolumn. Up to now, a great number of studies, including both theoreticaland application ones, have been conducted on the dynamics and controlof conventional two-end reactive distillation columns. For the totallyrefluxed reactive distillation columns, relatively scarce attention has beengiven so far. The totally refluxed operation mode makes the reflux drum interactsolely with the reaction operation involved and retards considerably thedynamics of the latter. The resultant great difference in process dynamicsbetween the reaction operation and the separation operation involvedleads frequently to under-damped responses with the degree ofunder-dampness closely dependent on the inventory control of the refluxdrum. With the tight inventory control of the reflux drum, the degree ofunder-dampness can be suppressed and this presents a favorable effect toprocess dynamics and controllability of the totally refluxed reactivedistillation columns. Two hypothetical ideal reactive distillation columnswith and without a side reaction, respectively, and a reactive distillationcolumn for ethylene glycol synthesis are employed to examine the uniquedynamics and controllability of the totally refluxed reactive distillationcolumns.The results obtained are in good accordance with the aboveinterpretation. The current work reveals the general behaviors of thetotally refluxed reactive distillation columns and can be particularlyuseful in control system synthesis and design.