Energy, exergy and environmental analyses of a combined cycle power plant under part-load conditions

¹ Faculty of Mechanical and Energy Engineering, Shahid Beheshti University, Tehran, Iran
² Department of Renewable Energies, Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran

^a Corresponding author: mohammadhosein.ahmadi@gmail.com

Received: 5 January 2016
Accepted: 14 March 2016

Abstract

The aim of this study is to evaluate the performance of combined cycle power plants in full and part-load operations in terms of energy, exergy and environment. The environmental analysis is performed using life cycle assessment method. Two different strategies are selected to control the gas turbine under part-load conditions, including Turbine Exhaust Temperature (TET) constant and Turbine Inlet Temperature (TIT) constant modes. Results show that gas turbine has a higher efficiency in TET constant mode. But, combined cycle shows a better efficiency in TIT constant mode. Exergy analysis results show that combustion chamber has the highest rate of exergy destruction, both in full and part-load operation. With reducing the load, total exergy destruction of the plant is decreased which is due to lower fuel consumption. Also reducing the load by 50% leads to 2.47% and 6.36% reduction in exergy efficiency of the plant in TIT and TET constant modes, respectively. Therefore, in terms of energy and exergy, it is suggested to use the TIT constant mode for part-load operation of the gas turbine within a combined cycle. But in terms of environmental analysis, results show that more emissions are produced in TIT constant mode, due to higher fuel consumption.