How do you evaluate alternative distillation configurations for multicomponent separation?

Multicomponent distillation alternatives: Direct sequence - separate lightest component first, then next lightest. Indirect sequence - separate heaviest first. Complex configurations - side draws, dividing wall columns, thermally coupled. Evaluation criteria: Energy consumption - compare condenser and reboiler duties. Capital cost - number of columns, total stages, heat exchangers. Product specifications - achievability with each scheme. Operability - control complexity, startup difficulty. Selection methods: Heuristic rules (remove dominant component first, do difficult separations last). Shortcut methods (Underwood equations for minimum vapor). Optimization - formulate as MINLP problem. Dividing wall columns save capital and energy (up to 30%) but are more complex to operate. Always verify with rigorous simulation.