Semicontinuous, middle-vessel distillation of ternary mixtures

The operation of a semicontinuous middle-vessel column (SCMVC) that separat es a nearly-ideal ternary mixture is analyzed MVCs have a large vessel betw een the rectification and stripping sections. In traditional batch rectific ation or stripping, a still is charged and distillate or bottoms products a re removed leaving heavy or light concentrates in the still, respectively. bl contrast, the middle vessel of an MVC is charged anti, similar to a cont inuous process, both distillate and bottoms products are withdrawn. The pro cess separates nearly-ideal ternary mixtures into three nearly-pure! specie s, with the intermediate-boiling species concentrating in the middle vessel , and the light and heavy species concentrating in the distillate and botto ms products, respectively. Shortcut methods are adapted to determine the mi nimum number of trays and minimum reflux ratio Alternative control configur ations are considered to achieve suitable performance throughout the campai gn. Two LIE configurations are shown to be suitable for this process, with the middle vessel decoupling the composition control loops and permitting d ual-composition control with little interaction. Simulations confirm that d ifficulties encountered when using a DB configuration for the dual-composit ion control of a continuous column do not occur for a SCMVC.