Shortcut models for retrofit design of distillation columns

Shortcut models are well established for grassroots design of distillation columns and have been widely applied. However, no shortcut models are available that address retrofit. Shortcut models are quicker to solve, do not have significant convergence problems and are more robust than rigorous models for column optimization. In particular, shortcut models for retrofit would be valuable for evaluating retrofit design options, for improving the performance of existing distillation systems (columns and heat recovery systems) and can be combined with detailed heat-integration models for optimizing existing heat-integrated distillation systems. This paper presents retrofit shortcut models for design of both reboiled and steam-stripped distillation columns. These models are primarily based on a modified Underwood method, the Gilliland and Kirkbride correlations, the Fenske equation and the material balances. The retrofit models are applicable for simple distillation columns, sequences of simple distillation columns, and complex distillation configurations, including columns with side-strippers and side-rectifiers. The models fix both the column configurations and the operating conditions, including steam flow rates, and calculate the product flow rates, temperatures and compositions, and the various heat duties. A comparison of the model results with those of rigorous models of existing distillation columns is presented to validate the model.