Investigation on Distillation Column Sequence and Heat Integration Effects in Methanol to Propylene Separation Unit: An Economic Optimization Study Based on Pinch and Exergy Analysis

To study the simultaneous impacts of distillation column sequencing and heat integration on the Methanol to Propylene plant's economy, different distillation sequences for three components separation have been examined. In this study, optimization has been done by considering Total Annual Cost, TAC, as an objective function and the independent variables, including the number of trays, distillation column pressure, and temperature levels of refrigeration cycles, by using the Genetic Algorithm, GA. In order to provide an insight into heat integration's detrimental effects on TAC, optimization has been performed with and without heat integration. Analysis of the optimization results indicates that heat integration can reduce the TAC of the separation unit by nearly 50%. Also, scrutinized interpretation of configurations over the optimization results leads to the proposition that the thermal coupling of the direct sequence, with TAC of 238,000$ would exhibit the utmost performance for light gas separations, which would be more than 10% improvement compared with the simple direct. Furthermore, the application of the proposed 4-component separation unit reduces TAC by around 10% compared with the industrial plant. In this regard, an optimization framework has been presented for the systematic design of integrated below-ambient temperature separation units.