No abstract

Interstage backmixing is encountered as entrainment in many distillation columns. Bidirectional backmixing is common in liquid-liquid extraction. These effects, which reduce the effectiveness of a separation process, may interfere with its operation even to the extent of shutdown. The design engineer and process operator need to recognize the effects of backmixing and must quantify them to take effective countermeasures. A procedure is developed which describes the effects of interstage bidirectional backmixing in multistage separations. It is implemented on an existing simulation for multicomponent distillation and is used to show the effect of backmixing on product purity as well as on the temperature and bulk flow profiles within the column. These profiles are compared with profiles generated by the specification of nonequilibrium stages to obtain the same product purity. The designer may then identify backmixing and nonequilibrium effects independently and allow for them quantitatively in his design.