Controllability analysis of thermodynamically equivalent thermally coupled arrangements for quaternary distillations

It has been proved that thermally coupled configurations can lower the energy consumptions around 30% in comparison to conventional distillation schemes for the separation of ternary mixtures. These potential energy savings have motivated research efforts on thermally coupled configurations for four or more component mixtures. Besides the significant energy savings that they have in contrast to conventional distillation sequences, one distinct feature of a thermally coupled configuration is that there is the flexibility to rearrange the column sections among the thermodynamically equivalent structures. A thermodynamically equivalent structure is a distinct conceptual design in terms of the column equipment and their interconnections, which provide the opportunity for optimal equipment design, as well as for the improvement of the dynamics and operability of the thermally coupled configurations. In this paper, a detail dynamic analysis of the thermodynamically equivalent structures for four-component mixtures is presented. The simulation results for the various cases of study have shown that the thermodynamically equivalent structures have different dynamic closed-loop responses in. contrast to the corresponding original thermally coupled configurations. It has been observed that the dynamic responses depend on the thermodynamically equivalents structures and their corresponding counterparts of the original thermally coupled configurations. Therefore, for a thermally coupled configuration with substantial energy savings, it is significant to compare the dynamic responses of the thermodynamically equivalent structures to find the optimal solution in terms of both energy consumption and closed-loop dynamic performance. (c) 2007 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.