Exergy analysis has shown to be an efficient tool for process optimization and understanding. An exergy analysis has been made of the Akzo Nobel vinyl-chloride plant at Rotterdam, the Netherlands using Aspen plus TM. The exergy content of the streams is calculated using ExerCom (licensed by Stork Engineers & Contactors b.v.) and processed using specially developed routines, The results of this analysis are shown in an Exergy Flow Diagram. The exergy flow diagram gives a clear picture on how the exergy is lost through the process. To improve the clarity of the diagram, only the net chemical exergy changes over the process units are shown. The exergy flow diagram shows those units which are best suited for optimization. Several optimizations have been compared on the basis of exergy loss reduction and operating costs reduction. The implementation of the optimizations to the current process is often economically unattractive, because the investment cost for the placing of new units in the current plant is high, compared to implementing it in a new plant. Therefore, exergy analysis for optimization is best applied during the development of a new process. However, exergy analysis of an existing process has shown to be an efficient tool to critically examine the process energy use and to test for possible savings in primary energy consumption.