Exergy analysis and annual exergetic performance evaluation of solar hybrid STIG (steam injected gas turbine) cycle for Indian conditions

The STIG (steam injected gas turbine) cycle offers a way for increasing the power, efficiency and NO_x reduction in gas turbines by injecting steam into the combustor. The present exergetic study is to investigate the influence of compressor PR (pressure ratio), TIT (turbine inlet temperature) and SAR (steam to air ratio) on the solar hybrid STIG cycle. Exergy analysis was performed for four cases based on the parameters of real gas turbines. Annual exergetic performance is also presented for the sites Indore and Jaipur in India under constant and variable power modes. The analysis suggests that the steam injection does not affect the performance of compressor. The total exergy destruction in the cycle increases with SAR and TIT. The exergetic efficiency also increases in the range of 40%-54.2% with SAR up to 0.9. The magnitude of exergy destruction in all components in the cycle (except compressor) increases by increasing SAR. Nevertheless, largest component of exergy destruction in the combustion chamber increases with SAR and TIT about 53% at SAR 0.9. The exergetic efficiency of combustor increases from 74.5% to 81.8% with increasing SAR from 0.3 to 0.9. The exergy destruction in the turbine increases considerably with compressor pressure ratio, sparingly with SAR and independent of TIT. The exergy destruction in the SH (super heater) is less compared to the economiser in the HRSG (heat recovery steam generator). The contribution of solar energy (exergetic solar fraction) is more sensitive to TIT and SAR than PR. It is noticed that increase in turbine outlet temperature, led by PR and TIT, decreases the exergetic solar fraction, and the cycle exergetic efficiency improves as the exergetic solar fraction increases, which leads to an improved performance device. The second largest percentage of exergy destruction is in the flue gas condenser to recover water for recycling, and the heat removed from the condenser is lost to the surroundings by cooling air. The annual values of exergetic solar fraction and exergetic efficiency at Indore are higher than Jaipur in both constant and variable power modes of operation.