Performance enhancements and NOx emission reductions using novel exhaust-driven hybrid gas turbine inlet air-cooling techniques

Abstract

For combined cycles, gas turbine inlet air-cooling (GTIAC) increases the mass flow rates of both air and the generated steam of the heat recovery steam generator and hence power output. The introduction of exhaust gas recirculation (EGR) to reduce NOx emissions necessitates the application of GTIAC to overcome the adverse effects of gas turbine (GT) inlet air heating that accompany EGR. For a hot-humid climate, the r5egular cooling methods consume a significant amount of energy while desiccant and inlet-fogging are not effective. The main purpose of this study is to introduce innovative exhaust-driven hybrid GTIAC techniques that can reduce effectively the inlet temperature of the combined cycle in a hot-humid climate without consuming a substantial amount of energy and examine the effects of applying such techniques on the performance and NOx emissions. In this paper, a thorough analysis for the effect of increasing ambient temperature ( To) and relative humidity ( RHo) on the performance and NOx emissions of the air-cooled GT combined cycle (ACGTCC) is presented and the novel exhaust-driven hybrid (NE-DH) GTIAC systems of desiccant-ejector, ejector-refrigeration, and desiccant-ejector-refrigeration are applied to ACGTCC and optimized for maximum power output. The 1-D model at the double choking was used to model the performance of the ejector GTIAC technique. The results indicate that applying NE-DH GTIAC techniques results in gains in power, which vary between 0.31% and 0.6% per °C rise in To and an efficiency improvement of up to about 0.5 percentage point and significant reductions in both capital and maintenance costs compared with applying the refrigeration GTIAC system. The introduction of ejector and desiccant cooling decreases NOx emissions further and adds no additional equipment cost if implemented together with EGR or some CO2 capture techniques. A suggested plan for GTIAC that reduces NOx emissions by up to 25% is presented.