SYNTHESIS OF HEAT INTEGRATED NONSHARP DISTILLATION SEQUENCES

This paper addresses the synthesis problem of separating a multicomponent feed stream into several multicomponent product streams of given compositions using nonsharp distillation columns while considering heat integration options. A general superstructure is proposed that contains all possible sequences (by allowing all alternatives for stream splitting, mixing and bypassing) and allows heat integration between the condensers and reboilers of various columns. The pressure of each column, as well as the key component recoveries, are treated explicitly as optimization variables. The mathematical model for this superstructure is a mixed-integer nonlinear programme (MINLP). This formulation is solved using a two-level decomposition approach in which the material balance equations are solved in an outer loop while the heat integration options are optimized in an inner loop. The proposed approach is illustrated with two examples.