Operation of Homogeneous Azeotropic Distillation Column Sequences

Abstract

A self-optimizing control concept is provided for sequences of three homogeneous azeotropic distillation columns with two recycles separating a ternary feed of a 020 mixture that has two simple distillation regions that are separated by a residue curve boundary. Studying a case with reduced complexity (columns of infinite length operated at infinite reflux), one of the two recycles (the entrainer recycle) is identified as the key manipulated variable for ensuring optimal operation of the sequence. Different setups of the scheme have different optimal feed regions. The theoretical results are illustrated with rigorous simulations of a 020 mixture: methanol (which acts as an entrainer), 2-propanol, and water. Dynamic simulations confirm that the process operates robustly by using the (L/D)Q R scheme for the individual columns and one additional control loop that controls the methanol (entrainer) composition of the distillate by manipulation of the overall feed of one column. Dynamic simulations also confirm that column profiles can cross residue curve boundaries, distillation boundaries, and even azeotropes if the feed composition is changed such that a column profile is only feasible in the other distillation region.

Residue curves map analysis for tert-amyl methyl ether synthesis by reactive distillation in kinetically controlled conditions with energy-saving evaluation

“…(4) is fulfilled for the hybrid reactive distillation column when the heat generated by the chemical reaction is taken into account. The deviation from the values obtained by simulation, introduced by the simplifications used in the N/N analysis (the heat of the reboiler is proportional to the distillate flow rate), shows that the reboiler duty is not directly proportional to the distillate flow rate, but for the evaluated cases, it was obtained that a lower distillate flow rate leads to a lower reboiler duty [28]. The hybrid reactive distillation column results are presented in detail.…”

“…The potential importance of this method was reconsidered by Bekiaris et al [23] which led to its much use [24]. The method was extended to heterogeneous systems [25], hybrid distillation columns with reactive and non-reactive sections [26,27], process synthesis for finding and ranking feasible separation schemes according to energy consumption, [28] and studying the influence of recycle streams [29]. N/N analysis is able to take into account the energy savings in the early steps of distillation process design and can be used to evaluate new opportunities with the existing distillation systems.…”

Modeling of Distillation Processes

“…The N/N-analysis has been systematically used for studying homogeneous azeotropic and heteroazeotropic distillation. Further, it has been shown that this method can also be applied to distillation sequences [9,10,18].…”

∞/∞-Analysis of heterogeneous distillation processes

“…Therefore, it has been systematically used for studying homogeneous and heterogeneous azeotropic distillation (Bekiaris et al, 1993;Müller and Marquardt, 1997;Müller, 1998). Further, it has successfully been applied to processes with more than one unit operation in a flow sheet (see e.g., Laroche et al, 1992;Esbjerg et al, 1998;Güttinger and Morari, 1996;Blagov et al, 2000;Nazanskii et al, 2001;Ulrich, 2002;Ulrich and Morari, 2003;Bonet et al, 2007). The stream table of a process resulting from ∞/∞ -analysis is, despite its inherent strong assumptions, often a good approximation of the stream table obtained from corresponding simulations based on the equilibrium stage model (Ryll et al, 2006;Grützner et al, 2007;Burger and Hasse, 2013).…”