CALCULATION OF PARAMETRIC SENSITIVITY IN BINARY BATCH DISTILLATION

This paper provides a comprehensive analysis of parametric sensitivity of batch distillation operations to perturbations in the feed composi tion. Three column arrangements are considered: batch rectifiers, batc h strippers and total-reflux columns. The perturbation dynamics is par ameterized in such a way as to allow the analytical calculation of the sensitivity function in the whole composition range, for both sharp a nd non-sharp separations. This makes it possible to determine a priori which operating conditions and system parameters favor sensitivity of the nominal state variable profiles, and to calculate to which extent parametric sensitivity is exhibited by a certain batch distillation o peration. For conventional batch rectifiers, it is shown that there ex ists a limiting value r(top) of the reflux ratio above which there is a 'sensitive' operating region characterized by a linear increase of t he sensitivity function with respect to the concentration of the heavy component in the reboiler; the higher the reflux ratio, the wider thi s sensitive operating region. For operations with r < r(top), the sens itivity function is independent of the reflux ratio. For batch strippe rs, it is found that sensitive and non-sensitive operating regions are located somewhat symmetrically with respect to the case of batch rect ifiers. However, the sensitivity function profiles are not symmetrical to those exhibited by regular batch columns. Finally, for columns ope rated at total reflux with a 'balanced feed', it is shown that if the feed is 'very' light or 'very' heavy, the transient behavior of the bo ttom composition sensitivity function is either always increasing or a lways decreasing. The parametric sensitivity in total-reflux operation s appears higher than the one exhibited in finite-reflux-ratio operati ons. (C) 1998 Elsevier Science Ltd. All rights reserved.