Análise de exergia de uma usina termoelétrica que opera em ciclo combinado

Abstract

In this study, an exergy analysis was developed in a thermoelectric power plant that runs in combined cycle, Brayton and Rankine, with two sets of gas turbines and a set of steam turbines, with 326 MW of installed power. Using the data collected directly from the plant control system, such as pressures, temperatures and flows, it was possible to evaluate the main installed equipments operative conditions: air compressors, combustion chambers, gas and steam turbines, boilers and condenser. Thereby, it was verified that both gas turbines, which are of the same model, operate under similar conditions, with small differences between them. Furthermore, the combustion chamber showed itself as the equipment with the highest exergy destruction levels, with 65.93% out of the total power plant and nearly 80% of Brayton cycle losses, with also only 78.61% of exergy efficiency for the first machine and 78.69% for the second one. In Rankine cycle, it was verified that both boilers developed significant losses to the process and, analyzing these elements, a considerable variation between them both was noticed, since the number 01 boiler operates with 23.19% higher exergy destruction than number 02 boiler, which represents a deviation worthy of more precise studies. Both boilers represent 60.16% of the total useful energy lost in Rankine cycle but 10.17% of the plant total. Moreover, a steam quality of 92% was found at the steam turbine exhaust, with evident damages to this equipment, which revealed recent erosion failures at low pressure blades stage. The condenser was the equipment with the plant worst exergy efficiency, with only 59.15%, while the turbines and compressors had values above 90%, at least. Sankey’s Diagrams were built to improve the exergy flow visualization in both thermodynamics cycles.