Insights on the dynamic behavior of thermally coupled distillation columns implemented on processes with recycles

Thermally coupled distillation systems can provide significant energy savings with respect to the energy requirements of conventional distillation sequences. Their analysis, however, has been typically carried out in isolation of the rest of the process under which these separation systems are to be implemented. In this work, a plantwide control analysis of a thermally coupled distillation system with a side rectifier implemented within a reactor-separator-recycle (RSR) system is presented. The energy implications and dynamic performance of such implementation are discussed. Two case studies are analyzed, one based on an ethylbenzene process and the other one on a benzene chlorination process. Although these processes show different details on their control structures, the results show that in both cases the energy savings provided by the thermally coupled structure can be obtained without a deterioration on the overall process operability.