Side draw optimisation of a high-purity, multi-component distillation column

Distillation columns with side draws are widely used in the process industry to refine crude methanol into high-purity methanol. Historically, industrial methanol manufacturers have concentrated on meeting strict product specifications, while methanol yield and reboiler duty optimisation has often been neglected. In this work, a steady-state model of an industrial high-purity multi-component methanol distillation column was developed using a commercial process simulator. To achieve higher recovery at optimal reboiler duty, the side draw location and side draw mass flow rates were identified as two important factors. It was determined that a combination of lowering the side draw location while reducing the side draw mass flow rate will lead to the most optimal outcome. A design of experiment was also carried out to evaluate the stability of the column at recovery rates of 97.7% (current recovery) and 99.5% (proposed high recovery). Disturbances in the feed stream were identified as having the greatest effect, while the product purity was observed to become more sensitive towards all disturbances when operating at an enhanced recovery. (C) 2016 Curtin University of Technology and John Wiley & Sons, Ltd.