The scheme of coal-fired power plant selected for investigating energy and economic impact of feedwater repowering is shown in Fig. 1. The system, simulated using Gatecycle software [27], comprises a subcritical fossil boiler, high, intermediate and low pressure steam turbines (HPST, IPST, LPST), a condenser and a feedwater heating system, including three low-pressure (LP) and three high-pressure (HP) feedwater heaters with an interposed deaerator. Feedwater heating system preheats water from the condenser up to 242C, thanks to bleedings from steam turbines. At design conditions, the ST plant capacity is 300 MW, while net efficiency and specific CO2 emissions are 42.5% and 742.8kg/MWh, respectively. Based on cost assumptions previously described, COE is approximately 74.9$/MWh. Table 3 summarizes the main operating parameters and energy and economic performances of baseline ST plant. Feedwater repowering is operated by integrating a gas turbine and two gas–water heat-exchangers (HX2 and HX3) that preheat a fraction of feedwater, thus partially replacing regenerative heaters. As shown in Fig. 1, HX3, fed by exhaust flue gas from a gas turbine, preheats a fraction kHP of water from deaerator up to 250C; HX2 receives the exhaust flue gas from HX3, preheating a fraction kLP of feedwater from the condenser outlet up to 140C.