In recent years, the environmental concerns and the need to improve the competitiveness of existing coal-fired power plants have renewed the interest for the repowering option. Repowering techniques based on combustion turbines allow to increase thermodynamic performances of the steam power plant, as well as to reduce emissions of greenhouse gases, due to efficiency improvement and partial fuel-shift from coal to natural gas.

This paper aims to evaluate performances of feedwater repowering of a coal fired power plant, considering various steam turbine overloads. Two types of analysis are here proposed. First, thermodynamic and environmental benefits of feedwater repowering are evaluated in terms of efficiency gain and CO2 emission reduction, with reference to the steam power plant only. Then, effects of the integration of a gas turbine into the existing coal fired power plant are highlighted. Different feedwater repowering options, varying the operating mode of the coal fired power plant, are compared from the energy, economic and environmental point of view. The attention is focused on performance parameters of the integrated steam-gas power plant, as well as on marginal indices defining the efficiency and unit cost of electricity of the additional power production.

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