Repowering combined cycle power plants by a modified STIG configuration

An innovative repowering concept for combined cycle power plants is presented. The design concept consists in adding one or more gas turbines to the combined cycle, integrated by steam injection into the existing gas turbine. The steam is produced in a simplified heat recovery steam generator fed by the additional turbine’s exhaust gas. The scheme is quite simple and easy to adapt to various types of combined cycles. The efficiency of the repowered plant compares favorably with that of the original combined cycle and far surpasses that obtained by simply adding the gas turbine with no integration. Furthermore, the additional gas turbine enhances the plant operating flexibility as any power output intermediate between the original and the repowered capacity can be readily attained with no significant efficiency penalty. A thermodynamic and economic evaluation of the system feasibility is presented.