Exergy analysis of the semi-closed gas turbine combined cycle (SCGT/CC)

In the present paper, an exergy analysis of the SCGT/CC cycle is presented. Exergy destruction has been analysed at the component level in order to identify the critical plant devices, considering several operating conditions. The power-plant configuration is similar to that presented in previous works, with the possibility of total or partial water injection in the combustion chamber at peakload conditions. Combustion, heat recovery steam generator (HRSG), water injection/mixing and water recovery system are the main sources of losses, representing globally more than 80% of the overall exergy destruction. The second-law efficiency ranges between 49% and 53%, moving from the fully injected to the not injected condition. These values are close to those of standard open cycles, which means a good potential for the SCGT/CC cycle, which has several advantages from the point of view of containment of emissions and capability of peakload shaving. Peakload operation (with partial or total water re-injection) involves additional waste of exergy, but is attractive as it can be very extended for this plant configuration. Some critical components, such as condensing heat exchanger, show some sensitivity to the operating parameters, which however only marginally affects the cycle performance. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.