Control properties of thermally coupled distillation sequences for different operating conditions

The understanding of the dynamic behavior of distillation columns has received considerable attention due to the fact that distillation is one of the ost widely used unit operations in chemical process industries. Thermally coupled distillation sequences (TCDS) can provide significant energy avings with respect to the operation of sequences based on conventional distillation columns. TCDS exhibit a complex structure, with recycle treams, that appear to affect their controllability properties. One potential solution to this problem has been suggested through the operation of CDS under conditions that do not provide minimum energy consumption. The basic idea is that if one changes the operation point, the control roperties might change as well. In this work, we analyze the dynamic behavior of two TCDS structures under different operating points, including he one with minimum energy consumption. The control analysis properties are analyzed with the application of the singular value decomposition echnique at zero frequency and closed-loop dynamic responses using standard PI controllers. The results show that the controllability properties f distillation sequences may change significantly depending on the selected operation point. 2006 Elsevier Ltd. All rights reserved.