Distillation Cascades Based on Differential Vaporization and Differential Condensation Stages. II. Four- and Six-Stage DCDV Cascades and Hybrid Cascades Containing DV Reboilers and DC Condensers

Abstract

The conceptual design for N-stage cascades based on the differential condensation (DC), and differential vaporization (DV) processes is presented. Four and six stage “no-mix” and constant recycle DCDV cascades have been modeled to separate an arbitrary binary feed. The study suggests that cascades based on the differential processes could be significantly more efficient than cascades based on equilibrium stages (ordinary distillation). In no-mix DCDV cascades, all stage separation factors are equal and significantly greater than the equilibrium stage separation factors (i.e., relative volatility). In constant recycle DCDV cascades, the DV reboiler and DC (partial) condenser stages have stage separation factors much higher than the relative volatility and are significantly greater than the separation factors for the interior DCDV stages, although the stage separation factors for the interior stages are still higher than the relative volatility. Constant recycle hybrid cascades containing DV reboilers and DC condensers coupled with equilibrium interior stages are more efficient than constant recycle ordinary distillation cascades containing the same number of stages, especially for systems with higher relative volatility that require fewer stages. For systems with lower relative volatility (greater number of stages) the difference in performance between the hybrid and ordinary distillation cascades is less pronounced.