Exergetic and exergoeconomic analysis of selected gas turbine power plants in Nigeria

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Analysis of power generation systems is of scientific interest and also essential for the efficient utilization of energy resource. The most commonly used method for analysis of the energy conversion process is the first law of thermodynamics - especially for computation of work and heat exchanges as well as thermal efficiency. However, there is increasing interest in combined utilization of both the first and second laws, using such concepts as exergy and exergy destructions in order to evaluate the efficiency with which the available energy is utilized. In this study, a thermodynamic analysis and performance of eleven selected gas turbine power plants in Nigeria was carried out using the first and second laws of thermodynamics and economic concepts. Thermodynamic modelling of industrial gas turbines in power plant applications was performed using a computer code developed specifically for simulation purposes with the Matlab software. Exergetic and exergo-economic analyses were conducted using operating data obtained from the power plants to determine the exergy destruction and exergy efficiency of each major component of the gas turbine in each power plant. The exergy analysis confirmed that the combustion chamber is the most exergy destructive component compared to other cycle components as expected. Furthermore, the exergy efficiency of the combustion chamber is less than that of any other components of the gas turbines studied, which is due to the high temperature difference between working fluid and burner temperatures. The percentage exergy destruction in combustion chamber varied between 86.05 and 94.6%. In addition, it was found that by increasing the gas turbine inlet temperature (GTIT), the exergy destruction of this component can be reduced. Exergo-economic analysis showed that the cost of exergy destruction is high in the combustion chamber and that increasing the GTIT effectively decreases this cost. The exergy costing analysis revealed that the unit cost of electricity produced in the plants ranged from 3.78 cents/kWh (N5.67/kWh) to 5.86 cents/kWh (N8.79/kWh). An examination of the effects of design parameters on exergy efficiency showed that an increase in the air compressor pressure ratio and GTIT increases the total exergy efficiency of the cycle.