Homogeneous Azeotropic Distillation. 1. Design Procedure for Single-Feed Columns at Nontotal Reflux

Abstract

Residue-curve and distillation-line maps are useful tools in the design of azeotropic distillation sequences. In this work we make use of residue-curve and distillation-line maps to develop a procedure for the design of single-feed columns at finite reflux. The procedure is noniterative with respect to the reflux and boil-up ratios, instead using an 'operation leaf' formed by the total and minimum reflux conditions. The operation leaf bounds the possible liquid composition profiles in a column section and is calculated from the product composition. The overlap of operation leaves is a necessary and sufficient condition for column feasibility. Special cases of operation leaves where the liquid composition profile strays outside the leaf are also presented. 'Open leaves', where the product distillation lines or residue curves and the pinch-point curves end at different nodes are introduced. These open leaves can be used to facilitate the crossing of total reflux boundaries at finite reflux using side-column flow sheets. The use of side condensers and reboilers is shown to reduce the capital penalty in the crossing of total reflux boundaries. The concept of operation leaves can be applied to the retrofit or reuse of existing distillation columns by defining stage composition lines that bound the composition space within the leaf achievable with a given number of stages.

Sectional and overall reachability for systems with S‐shaped distillation lines

“…An algorithm has been proposed by Castillo et al 1998 to evaluate column feasibility for homogeneous azeotropic systems. This procedure is based on the principle of finding all feed compositions that will produce a specified product in a column section.…”

“…The other approach, which has received more attention lately, identifies all feed compositions that will produce a specified product when fed to a column Ž section Pollmann and Blass, 1994;Westerberg and Wahn-. schafft, 1996;Castillo et al, 1998 . These techniques will reliably determine column feasibility as long as all reachable compositions are contained between the minimum and total reflux bounds. However, it has been Ž .…”

“…However, it has been Ž . noted Castillo et al, 1998 that sectional profiles for columns can extend beyond these extreme operating limits in regions Ž of composition space where the total reflux curves distillation lines for a staged column and residue curves for a packed . column take on an S-shape.…”

Production Zone Method: a New Non-ideal Shortcut Method for Distillation Column Design

“…Based on the operation leaves of Castillo et al (1998) the method uses production segment rather than completely specified product which eliminates any sensitivity to the composition of the minor products. It has two aims.…”

“…This is for example the case with the Rectification Body Method (Bausa et al, 1996) and another method developed by Thong and Jobson (2001). Based on the operation leaves of Castillo et al (1998), the aim of the presented method called Production Zone Method (PZ method), concerns the feasibility of the separation in the acquisition of a column pre-design. The method uses production segment rather than product with completely specified composition which avoid being sensitive to the composition of the minor product.…”