Comparison of a conventional two‐column demethanizer/deethanizer configuration requiring refrigerated condensers with a nonconventional column/rectifier configuration

Abstract

AbstractBACKGROUNDMany researchers have demonstrated the economic advantages in some separations of non‐conventional distillation configurations such as the use of a side rectifier or a divided‐wall column. Most of the systems studied in the literature appear to have operating pressures that permit the use of cooling water in the condenser. This inexpensive heat sink means that the energy economics depend almost solely on reboiler duty. This work explores the situation in which expensive refrigeration must be used in the condensers. The numerical example is the production of natural gas liquids (NGL).RESULTSThe resulting cryogenic reflux‐drum temperatures (−80 °C in the demethanizer and 12 °C in the deethanizer) require expensive refrigeration. Therefore, the economics depend on both reboiler duties and condenser duties. Two cases are studied. The first uses the product specifications proposed in a literature paper, which correspond to very high recoveries of methane and ethane. The second case uses more reasonable recoveries and also finds the optimum recovery for propane.CONCLUSIONSIn the first case, the conventional two‐column configuration is more economically attractive than the non‐conventional column/rectifier configuration because of lower refrigeration costs. In the second case, the opposite is true because the refrigeration load is much smaller. © 2015 Society of Chemical Industry