Thermodynamic performance analysis of state of the art gas turbine cycles with inter-stage turbine reheat and steam injection

Inter-stage turbine reheat is an effective gas turbine retrofit which can easily be used with simple and steam injected (SI) gas turbines as well. Although reheat provides higher inlet temperatures for HRSG in SI cycles and also increases net work output significantly, reheat combustor increases fuel consumption and thermal efficiency may still decrease. Therefore effects of reheat and steam injection in terms of thermodynamic performance require a detailed thermodynamic investigation. In this regard, simple, reheat, steam injected (STIG) and reheat steam injected (RHSTIG) gas turbine cycles are compared using the state of the art cycle parameters. Optimal performance parameters are determined using a new comprehensive cycle model which simulates combustion process regarding 14 exhaust species. It has been found that reheat provides a significant improvement on the cycle net work but it is not suitable for cycles having low pressure ratios if the only concern is maximum thermal efficiency. Results show that a good compromise between the maximum net work and maximum thermal efficiency is observed when reheat pressure is equal to the 0.4th power to the maximum cycle pressure. At this case, reheat provided 35.5% improvement in net cycle work with an efficiency penalty of only 5%.