Thermoeconomic optimization of a single-shaft gas turbine by varying working hours

Global primary energy consumption is growing through increased average energy use per person and world’s population. The percentage of alternative energy sources is increasing to meet most of the total global energy demand and to limit climatic effects of energy produced by fossil fuel. Therefore, the energy market scenario has changed in the last years. The renewable energy, that is unpredictable due to its irregular nature, causes a fluctuation of the global electricity produced and available. Gas turbines and power plants are obliged to operate in an intermittent mode in order to balance electricity variations and consequently to work for a reduced number of hours. Nowadays, the design concept of new gas turbine is focused on a thermoeconomic analysis because a best thermal efficiency does not imply an economic optimum in this energy market scenario. The aim of this paper is a thermodynamic and economic optimization of a large-scale (255.6 MW) single shaft gas turbine. Performances and costs of the gas turbine have been evaluated using the Energy System Modular Simulator 0-D code. Firstly, a thermodynamic analysis fixing the power output and varying turbine inlet temperature and compressor pressure ratio has been realized to maximise the gas turbine efficiency. Best thermal efficiency of 0.4250 has been obtained with a high-pressure ratio (38) and a turbine inlet temperature of 1484.5 K. Thermodynamic optimum is not a necessary condition for a minimum cost of energy that has been achieved with a pressure ratio of 26.3 and a turbine inlet temperature of 1500.5 K for base load applications. Thereafter, a sensitivity analysis of the number of working hours with respect to the gas turbine costs has been done to determine thermoeconomic optimum parameters for gas turbines that work to supply only peak load. The optimal values for 3000 working hours per year are a pressure ratio of 19.9 an efficiency of 0.4001 and a turbine inlet temperature of 1490.5 K. © 2018 University of Minho. All rights reserved.