A new methodology for the optimisation of feed conditions as well as the calculation of minimum reflux ratio of distillation columns is presented. The reversible profile approach used for saturated liquid feeds is extended to consider other feed conditions. For flashed feed, the liquid fraction of the feed stream is used to compute the column pinch conditions and the minimum reflux ratio. The modifications required for subcooled liquid and superheated vapor feed are discussed, and a procedure to estimate the minimum reflux for those conditions is proposed. The methodology presented allows the identification of the optimal feed condition, without having to resort to a full stage-by-stage procedure.
mininum reflux; near-reversible distillation; exergy analysis
