Economic Analysis of Separation Unit of Methanol to Propylene Production Based on Optimization of Refrigeration Cycles Using Pinch and Exergy Analysis

Abstract

In this study, optimization and economic analysis of the separation of light gases in the methanol to propylene, MTP, process along with refrigeration cycles design are performed, by using pinch and exergy analysis. In the course of the separation process optimization and refrigeration cycles design, by using a Visual Basic, VB, program and genetic algorithm, GA, rigorous distillation simulation is carried out, then streams information is employed to find optimum temperature levels, corresponding to tower condenser temperature, by minimizing the areas between the Exergy Grand Composite Curve, EGCC, and constant temperature levels of refrigeration cycles. Economic calculations were performed to obtain the lowest total annual cost, TAC, for refrigeration cycles, towers and other equipment. Two cases of the direct and indirect sequences are examined through the developed framework, inspection of their results represents that the operational cost has a significant contribution to the TAC. As a result, heat integration would reduce it by nearly 60%. Also, scrutinized analysis of the optimization results, especially by considering the TAC and its contributions, for the direct and indirect sequences, leads to the conclusion that indirect sequence would exhibit lower cost for light gas separation. The framework represented herein paves a way to the systematic design of integrated low-temperature separation processes with refrigeration cycles.