Exergy Analysis Applied to Separation Processes in a FCC Plant Using Computational Models

Exergy analysis is a useful technique that allows in deep discussion of energy utilisation in chemical processes. Furthermore, it helps to discover specific areas in the process subjected to energy degradation (Rivero, 2002). On this work, the results from the analysis to several cases of topology modifications in the separation section of a fluid catalytic cracking (FCC) in a refinery are illustrated. In the evaluated plant, it was found a high potential for energy optimization in the main fractionator column where exergy losses reached 105 GJ/h and cooling requirements were about 240 GJ/h. A reduction of 10 % in exergy losses, related to base case, is achievable in according to the proposed modification. Annual savings are estimated between 0.45 and 0.50 M USD/y, and reduction in pollutant emissions are calculated around 5,100 t CO(2)e. The methodology used, included the configuration of a wide process model in a commercial simulation software, the validation of the model by plant test run, the validation of the exergy computation algorithms from modelling applied to several operating scenarios. The model included the separation section of an FCC plant, starting from main fractionator, stripper, debutanizer, depropanizer, the compression system and liquid gas absorbers, as well as the heat transfer section.