| Summary: | In existing chemical processes, feed flow and composition changes, as well as product flows and purity changes are quite common and the retrofit of the process is often of more interest than its design. The discussion of retrofits will be divided into two parts. In the first, performance models are presented for simple columns. Explicit solutions for binary mixtures are obtained, but it is shown that the degrees of freedom prevent the generalization of the explicit solutions to multicomponent mixtures. In this case as an alternative to long computer simulations, collocation is suggested for performance models. Complex column alternatives for multiple feed and sidestream columns are also described and approximate models are developed for such configurations. Rigorous simulations confirm estimated savings of as much as 30% in operating costs. In the second part, a procedure for the systematic retrofitting of distillation systems is described. This consists of five levels, and is based on shortcut design and performance models for both simple and complex sequences. In the first two levels, minor operational changes are considered; subsequently major equipment rearrangements, replacements and the addition of parallel units are examined. The procedure considers minor changes at little or no incremental capital as well as major structural changes that involve applications of multiple feed columns, parallel units, sidestream and thermally-coupled columns.
|
|---|
