ABSTRACT
A stage in a separation process could, for instance, be a tray in a distillation column, a section in a packed absorption column, or a partial condenser or reboiler. An equilibrium stage is a contacting device-a vessel-in which two or more phases can mix thoroughly and interact with each other for a sufficient length of time until the number of moles of any component moving from one phase to another equals the number of moles of that component moving in the opposite direction, i.e., until no more net mass transfer takes place between the phases. The composition of each phase is then the equilibrium composition.
