SHORT-CUT TECHNIQUES AND ENERGY CONSERVATION FOR DISTILLATION COLUMN DESIGN

This work develops short-cut and energy conservation techniques for distillation column design. The objective is to analyze the application of the short-cut techniques and heuristics (rules-of-thumb) to preliminary design, and obtain simple relationships for the distillation models.;In the sequencing problem, a simple analytical criterion was developed which can be used to obtain estimates of the optimal sequence of distillation columns for the separation of ideal multi-component mixtures. Also, simple analytical expressions for calculating the optimal pressure of the system, the reflux ratio and the cost of a separation are presented. The results and a sensitivity analyses made for a ternary mixture indicate that the direct sequence is preferred in most of the cases. The approach is also extended to quaternary mixtures.;Finally, short-cut techniques are developed to estimate the number of trays, minimum reflux ratio and cost in more complex distillation schemes for ternary mixtures, such as sidestream distillation columns, with and without auxiliary columns. These schemes can give substantial savings compared with the conventional configurations for certain ranges of feed compositions.;Short-cut design methods and simple cost models are derived for conventional distillation and for some energy conserving distillation schemes for the separation of binary mixtures. Among the alternatives to conventional distillation columns, multiple-effect and vapor recompression are considered. The simple cost models are used to determine optimal reflux ratios and approach temperatures in the energy conserving distillation configurations. A thermodynamic analyses of the binary distillation schemes is done, and the concept of "distillation efficiency" is used to compare the performance configurations. Both the economic evaluation and the efficiency analysis, show that vapor recompression is preferred over the conventional system, especially in the case of closely-boiling mixtures. Of the various vapor recompression schemes, the reboiler-liquid-flashing alternative presents the most favorable performance.